As someone who has been used to post-release content for PC games since the 90's, after the DLC method was established I think that the value for what you pay for has gone completely down the shitter.
Small things, like a couple of new multiplayer maps and the likes, would typically be distributed for free separetely or included in a patch. If a more substantial amount of content was created it would be sold as an expansion pack for a decent price like $19-$29. Today we get things like the CoD map packs, 4 (where 2 of them are recycled from the previous game) for $15.
There are a few developers that haven't lowered the bar for their customers like Valve and Epic (barring Gears of War, but that's Microsoft's decision, not theirs). The Titan Pack for UT3 included a pretty generous amount of new maps and new game modes without costing a dime, as is the tradition with UT bonus packs. It was released on PC and PS3, but MS wouldn't have any of that on the 360. If it was released as paid DLC it would probably be priced at around $49 or something. Got to keep the XBL userbase blissfully ignorant, after all.