What started as the Team Fortress 2 nonsense store which allowed the purchasing of hats in a first person shooter(!), has progressed to a total overhaul of how Valve sell their products. Portal 2 is now fast becoming the flagship example, with, wiat for it, hats available for purchase, along with little flags and such. DLC (I feel a bit sick every time I say or type that) is the devil that you cant' avoid. If Activision put a human shit in a box and sold it as Call of Duty (or Modern Warfare, whichever they own) material DLC, for let's say £5 / $9, it's guaranteed they would make a profit. Call of Duty: Human Chemical Warfare in a Box.
Pretty much every game you buy now has this so called downloadable content, right from the game's release. There's no relevant analogy here, even the most coherent slashdot analogy wouldn't be able to ascribe to the bizarre concept of selling an entertainment product with parts loped off and sold along side it.
A great example is the add-on content to Railworks 2. A £25 game with £800(sic) of DLC. Have a look if you don't believe me. http://store.steampowered.com/app/24010/
Bottom line, there's a huge amount of money to be made on the DLC market and any game company would be stupid not to dip into that pool. And it's a damned shame.