"Coincidentally, How would you like it if someone stole the work you'd been doing for the past 5 years?"
Unlike Valve, I believe that it's more important to produce a quality product than to try to profit from "trade secrets".
I produce a shadow system for games which I sell.
While I obviously don't want the source code distributed, if it was, it wouldn't hurt my business much. Most people who want to use it would pay the nominal fee I charge.
In addition, when someone asks me how to make a shadow system like the one I've made, I give them a full and complete description of all the various optimizations I've done, explaining exactly how it works, and how sophiticated an algorthim it uses.
At which point, they realise that my system is so good that they'd have to spend months writing their own, and they choose to license mine for the nominal fee.
I even give away source code to major portions of my games for free. The only thing I don't really do is give away complete compileable versions of my game code, because I don't want someone producing a game which is 75% identical to mine.
I also share my art, and sound effects, if people ask for them. I am not particularly concerned about people competing with me. The market is big enough for everyone, and nobody is very likely to take my stuff and produce a game which is near identical to my own.
So, to answer your question, if someone stole what I'd worked on the past 5 years and used it, it wouldn't have much effect at all. The chances of them being stupid enough to release an exact copy of my games and attempt to sell them is slim to none. Worst that would happen is they'd have nice shadows and heads up displays and particle effects in their game.
And graphics do NOT game a game. So if Valve is so concerned about some pixel shaders, then maybe they've stopped concentrating on gameplay. And if they fail because of that, that's their own fault, and not the fault of someone getting ahold of their pixel shaders.