This is a classic example of Price Elasticity, and it's actually GOOD for gamers. Managing the demand curve is how game companies stay in business.
Price Elasticity is simple: different people are willing to pay more/less for the same thing. Gamers are already familiar with this; it's why prices drop over time. At launch a new game sells to people who think it's worth $60. Over time, the price drops so they can sell the game to people who don't think it's worth $60 -- first to the $40 folks, then the $30 folks, and finally the $20 folks. DLC is just another way to recoup the investment of making a game (and hopefully turn a profit). You create additional content, and sell it to the people who are willing to pay for it.
Complaining about content on the disc is just idiotic--who cares where it is? Would it be better if Bioshock 2 padded the 24kb with an extra 20mb? The only valid complaint (and the only complaint developers and publishers will listen to), is that the base game was unsatisfying or felt incomplete without the DLC. And I haven't heard a single person say that.