Well, it's not "my idea," it's basic marketing. Goods are priced at the level the market will bear.
Besides, I seriously doubt any game company will intentionally cripple a game, forcing you to buy downloadable content. That just isn't going to happen. I seriously doubt Microsoft would even LET that happen -- heck, they don't even allow titles to require the hard disk drive to be present, and Microsoft makes money from HDD sales.
Another thing to think about. Since developers can charge for downloadable content, they can spend time and money creating brand new content/features, knowing that they'll get a return on their investment. Which might lead developers to continue releasing new content long after release. You may see new content in quantities and of a quality level that you would not otherwise have seen.