You're hardly comparing like-with-like there though. I'd look again.
Magicka has extra levels available as DLC which do add to the core of the game. No, it doesn't add to the story or narrative, but that's because Magicka barely has one. Magicka is about running around maps and killing stuff. It's like complaining that the DLC for a driving game only adds new cars and tracks, and not cutscenes in between races.
Magicka does have some shiny equipment you can buy too, which are just pointless little trinkets... and so does Dragon Age. Both of them. The item packs for DA2 came out about a month ago and are significantly more expensive than the Magicka ones too I think.
And to address the crux of your argument, outwith of the games themselves, people get annoyed at the DLC that adds actual content as they feel like they have to buy it, whereas cash cow stuff can just be ignored (and I've said it before and will say it again: if the cost of my games can be subsidised by rich people that buy hats, then that's just fine with me).