That's partially attributed to Gamestop being so dominant. Unlike movies, games don't have theatrical runs to provide revenue before they hit the home market. When games come out, sales usually almost always drop only weeks after for the next thing. This is magnified even more with the ps3/360 combined total not yet equaling the ps2 install base in its prime years.
Companies feel they should get something from their games selling to more than one customer. That's why you see the rise of Gamestop exclusive preorder stuff that often becomes DLC later on anyways, as it helps encourage buying new. It's not a shock that some DLC evolved into targeting Gamestop new/used customers, but it's not just EA, and they have been on both sides of the dlc price/value spectrum in the past few years.