Yeah im sure games have to go through many channels in the releasing proccess, i think Demos are as much of a risk with any game not just RPGs and thats why they are dying out. Like people have said, if you dont like what you see in the demo, your less likely to buy the game and that can hurt sales big time, especially as word spreads from people who have tried the demo to people who havent, and then you get people not trying it at all.
Preorders, admittedly im a sucker for those as usually they do have those little 'extras' whether its some DLC, a extra few items or something physical. I always end up justifying it by saying its a way to thank the devs for the work they've done... but its quickly becomming like a disease. What we do get as 'extras' are slowly getting more and more...well...rubbish to be honest and people are diving in blindly and regretting it later. 
I trust BioWare to make something awesome with ME:A though, demo or no demo.
Demos are a gamble, sure, but there should be some degree of pressure in order to sanctify the quality of games and increase competition (e.g. "Whose release can be the highest quality?") in the gaming market.
As for paying for extra content as a way of saying thanks.... Well... I dunno. I don't see video game development as a service type of area. You know...like you bring in cookies to say thank you to the volunteer firefighters etc. That kind of thing.
Not that I think the game devs are my slaves and deserve zero gratitude, but I do think that, overall, video game consumers could stand to be a little more adamant about video game quality upon release. The only way that can be voiced is through the power of one's pocketbook. Buy games later rather than preorder - even if it's just a month or so later. Your money now holds higher value (due to interest) than your money a few weeks to a month or so from now. That's why preorder money is so valuable. The earlier the cash flow, the more interest is accrued.