I probably shouldn't feed into this too much, but I'll give it a shot. Valve doesn't need to put games on the PS3. They are making millions and millions off their games and their Steam service. They get buyout offers weekly, and turn them all down because they like being independent and running things their way. Valve has been a traditionally PC developer and they're making a lot of money on the PC. They're not a tremendously huge company so they have finite resources. Plus, they're working on Left 4 Dead 2, most likely Portal 2, probably Half Life 2: Episode 3, as well as updates to Team Fortress 2 and Left 4 Dead. So what they have to weigh is the cost of adapting the Source engine to the Cell processor that requires a lot of optimization to get processes to run smoothly and efficiently. They have to weigh the cost and manpower necessary to port their games to PS3 (given that the PC is their main focus, 360 is just easy to port over due to it's architecture) versus the amount that they can expect to sell on the platform.
For them it's just not worth it. It's not that they couldn't do it, it's just that they don't need to and don't want to. They're independent and can do what they want. If you really want to play their games, get a bunch of 3-4 year old PC parts and put yourself together a PC for a couple hundred bucks, or if you have about $500, put together a decent modern gaming rig that would run them at high settings (check the GAF threads for part info). So yeah, I'm tired of hearing people say that Valve is imcompetent or somehow inferior to Naughty Dog, Guerilla, or Insomniac. Each studio has their focus, and Valve's is PC. It's not like Newell is the first to criticize the PS3's architecture anyway, it's just that he's very outspoken about it and has made their stance well known.
And yes, this thread sucks.