@Eelectrica : Outside of MMO's that is rarely the case. DLC adoption rate for single player or MP is actually relatively small in the grand scheme of things. We're talking 20% in general. Hell even in MMO's not everyone gets the expansions, but in that you have a large community that the bulk do upgrade but its due tot he nature of that type of game. When your constantly running into people who're able to get to higher lvls with better gear then you, people tend to eventually make that jump.
With most other games that rarely happens. If they were to make it payed DLC with no microtransactions (that pay for the free DLC production), they would need a capability patch to allow people who advance further with new stuff to play with everyone. And those people wouldn't get to play on there DLC maps with non-DLC people. Most games don't get capability patchs and end up heavily segmenting there online player base. Obviously not much of an issue with single player only games - there's no direct interaction with the community DLC or otherwise while in the game.
As far as accidentally buying a pack I agree, the way it was done in ME3 was garbage. I didn't like the pure randomness and I didn't like the straight pay option being right there. But we have some information that seems to alleviate that in DAI. First they have a secondary currency you have to buy separately with real money for that. Now it may bring up a prompt if you accidentally hit the buy with platinum to ask if you want to buy said platinum but at least it's an extra layer to help you realize the mistake.
2nd bit brings me to the random crap in ME3. Once you got a gun that was it, that was the unlock. In DAI you get items from chest IN game, and also use gold to buy more chest out of a match. If you get stuff you don't like you can break it down for parts. The Crafting is in full swing in the MP as they've mentioned. That means you can make stuff you actually want, out of stuff you may of gotten you didn't want. And that, that right there, makes me a hell of a lot happier then dealing with how ME3 handled things.