Interesting, but matter of the fact is, Steam is big business for Valve and Microsoft having their own portal for selling software can and will eat revenue off of Steam. Valve are claiming this is bad for consumers, free the people enslaved by Microsoft etc, when in fact many of us are "slaves" of Steam. They're trying to future proof themselves and this is a sane business minded way to look at it but don't think for a minute that Valve are just doing this for charity, it's all about money. The fact that they ARE putting real effort in to the Linux Project shows that they are genuinely concerned that Microsoft in the end will eat up a considerable amount of their profits. Also, Microsoft are trying to get developers onboard by undercutting the industry standard fees for selling your apps on online "marketplaces". Microsoft is offering 80% of the profit of selling an app or game to the developer after they pass the 25,000$ line as opposed of most of the "competition" that only offers 70% of the profit however much they might sell.
Still, I think Valve should be careful not biting the teet that they feed off of. ;)
P.S I'd like to say that I love Steam. I have A LOT of games on Steam (many I haven't even had the time to install yet, *ugh*) and I can see why Valve are looking elsewhere with there business but what I don't like is how Gabe Newell keeps dissing Microsoft and saying things will get worse for the consumers, closed eco-systems are bad etc. That's just populistic BS, it's all about the almighty $, nothing more nothing less but saying that publicly won't create any popular sympathy for Valve. I don't like when people try to manipulate popular opinion by pretending that they care about people, you know, like just about every politician out there.
P.S I have to give Valve credit for getting Nvidia onboard considering the rather chilly relationship between the Linux community and Nvidia in the past, just ask Linus Torvalds: