After dumping buckets of money into Valve's little online service this holiday season, I got curious about how exactly they make money by charging things this cheaply. It's not exactly the same process as bulk distribution like Costco and it's not really Wal-Mart either. They basically just sell CD Keys and then wrap that up into this really handy update service with social networking. They have low overhead but not as low as their competitors. Instead, the reason Valve owns this scene is that waaaay back when Half-Life 2 came out, you had to install STEAM. They've had that policy for a while now with all their games. And it looks like it's paying off.
For some reason or another, the process reminded me of a perpetual motion machine that is supposed to generate infinite energy if you just set it up right. Prices go down, value inflates, prices go back up, sales continue. I'm not sure this would work for every single game out there, but something like Madden or Team Fortress 2 would be the prime candidates for perpetual value games.
On paper anyhow, these things never quite work like you'd expect.