Without DLC there wouldn't be any expansions.
This was why expansions died and the MMO formula took over for the RPG genre... After a title being on the shelves a year, guess what, no one was playing it anymore! They moved on. Expansion sales could not sustain a profit to development ratio (and anyone thinking any decent developer is making less than $75/hr is probably nuts or a bad developer... good devs are expensive and every game company wants the best).
DLC can be produced in much smaller time windows and allows a franchise to maintain a revenue stream that funds either future 'larger' expansions or a full blown sequel. In these modern times, I'm pretty sure you will be most likely to see a sequel in a two year time frame full of DLC than an expansion because, frankly, tech is changing too fast to just add on to an existing engine after it's been in the wind for a year.
Do I agree with the cost of DLC (particularly the small kind like WK, let's say, because there are some really good long dlc's out there comparable to strong expansions... Fallout 3 Broken Steel?)? Not always. I do think $5 is a little steep for something rumored to be a one hour content bonus which in reality means 10-20minutes probably (all rumors and probably not true as it is a little... odd... that it would be that simple and short). That should be a .99 add on, in my opinion. Same for the generic weapon/armor/whatever model upgrades and adds. Something like Shale is probably $5-10 fairly. But, it's business and they can get more so they do... They have to by law really. It's that magical spot on the supply vs. demand chart where the two lines meet... That's maximum price and that is the simple thing they are using to decide this stuff.
You can't compare the price to anything historically without considering the present value of money and the time to cost ROI. Looking back at the $30 the two NWN expansions each ran, that's probably closer to over $45 in today's dollars (that 3-4% per year really does add up!). The $5 D&D mods... Well, you get the picture. That's nine DLC's at $5 each and I'm sure much of the DLC for DA:O will be longer than an hour. It could very well add up to 20-30 hours of content for $45. -> We just don't know at this point. <-
The bonus is simple. Having DLC monthly or better keeps the game fresh and creates much better longetivity for the title. It trickles in little nuggets of love to keep people playing it over that year it used to take to do expansions instead of having them uninstall and hesitant to fire it up again. I'm not a patient person... I did get NWN's expansion; however, it was more because of the toolset and the ability to create persistent worlds. It was basically a freakin' MMO! So many different places to go play and socialize. I found a great 'world' that was fun and had good people and good DM's (I ended up being one of them) that ran a lot of great campaigns and constantly expanded things. It stayed fresh and popular. That's the only reason I made it until expansion time... If not for that aspect, no way I would have still been around. Only an MMO can do expansions like that anymore for that reason (no online persistent worlds with this DA:O toolset sadly).
Get as angry about it as you want but you are just contributing to early onset of all kinds of stress/anxiety related illnesses. Nothing can be done to change that supply and demand ratio unless you can successfully rally the _millions_ of troops to suddenly change their buying preferences. Better to just live within your means and your preferences and be happy with that (I agree it can be quite frustrating when you really love something as much as many seem to love DA:O and want a lot more but just can't have it).
Just remember... These gaming companies aren't evil. They have egos too! They want to look and play the best. No one wants to put out crap (it just turns out that way sometimes... look at MW2... wow.. what a step backward for such a good franchise! SP campaign is only 4.5hours!!!! Dated and played out graphics and shooter styles!? WTH is up with that right? Still cost full price for what should have been a $29.99 downloadable title on PSN or LIVE, in my opinion). Some companies are better at expressing this than others, i.e. Naughty Dog and how they have handled media and how they manage their office/studios (the results speak for themselves in Uncharted2, which by the way, EVERYONE should play if you are a console person as it is probably the best developed game this generation at the very least). I've digressed... But, my point is the same. Companies want to provide the best they can. It's not natural for them to want to 'screw over everyone' because they ARE everyone. They are consumers also. They are simply trying to find a way to maintain the viability of their business (and, yes, maybe the video games business model is way overdue for a work over; however, it ain't happened yet so until it does, which will probably take some big towers like EA/Ubi/Acti falling first, we are stuck with it).
The used games market is a serious problem (to just keep going while I'm typing because I love how we can all just blurt out our opinions to the world on the internets). It's not fair to say how DLC is bad and should go away then turn around and compare it to the used car market. Ford makes money on used car sales... They make A LOT of money still. Why? Because those cars need parts. They need labor that only dealers (thanks to overpriced proprietory computers and machines and tools) can provide. Ford makes money on every car it sells until the day it is melted down for scrap metal (and then they probably still make money because the recycled metal costs them less than mining new steel!). Once a game hits the used market it's monetary income dies. Gone. Poof. DLC is the 'parts' to keep that money chain moving with used market shoppers. It's the maintenance plan. I agree used DVD's are very similar to games; however, if you look at where DVD is going (particularly on Bluray) with internet enabling and bonus content, etc., it's the same thing the video game industry is doing. They are trying to create more content to sell (never mind movies already make money from royalties in other sources no matter what forever... too bad video games don't have showtime and hbo huh?).
Bottomline, DLC is here to stay, like it or not. The little bites of sometimes goodness are there to keep us nibbling on the fruits of developer labor. And, it works (for many anyway). It keeps us in the buying chain for a bit longer and when we leave it there is a little bit of love from those who buy our game used. Because of it's medium video games simply can not be compared to other products (cars and dvd's, in this example). They do not have the other revenue streams those products enjoy. They have to be creative to finance these games today (it costs WAY more to make them). At $49.99-$59.99 (more for collector's) it's a steal compared to the old $30 Atari games (about $80-100 in today's money!)... Yet, we get SO MUCH MORE. And, that is because of the creative geniuses at these development houses finding creative ways to help us help them keep making awesome games.
In the meantime, let's hope the toolset yields some strong results in the medium term and gives us some good playable stuff.