To be fair, even as a PS3 owner (and PC player for Valve games) I see their point of view.
They're primary a PC developers, and I'd reckon that most of their sales/income still comes from PC.
They operate Steam, which is actually a combination of Live, PSN and XBLA delivering both content delivery and community services - in a very real sense they are MS competition on PC for Live.
Their games are built on an in-house engine developed primary for PC.
Now, due to 360 architecture is is relatively easy for them to put games on 360. I hesitate to say everything the develop on PC results in a game on 360 for free, but it's clear the cost is fairly minimal next to the PC development anyway.
PS3 is a different story. Look at U3 when first put on PS3 (another PC orientated engine that underpinned Gears of War) - it didn't run too well.
So Valve have a choice, lose the revenue from PS3 but save costs and keep their engine support and development easier, or put in serious effort and ramp up for PS3.
Clearly, right now, they are comfortable to lose the revenue vs saving the costs. Valve are almost certainly cash rich, and I can see what they'd go that way. Remember titles like Half Life 2 sold over 6M at retail on PC plus apparently a fair bit in addition on Steam. Each HL2 episode is selling more than most full FPS titles. They are getting the income generated via steam, etc.
They have no pressing need to complicate their lives, even if it does mean missing out on probably a nice amount of PS3 based sales.
I admit its easier for me to accept this since I'm not missing out on the games as I play Valve games on my PC, but its a fair point and doesn't, I believe, come from any MS or 360 bias. Getting revenue from the 360 is easy for them - fish in a barrel you might say. The PS3 is a different story due to its architecture (which has clearly given all PC orientated developers a headache).
I don't think this means the PS3 architecture is wrong or the 360 is right. It simply means if you are a great PC developer the 360 is a piece of cake and the PS3 is not.