I may be a gamer and I actually own a good deal of Valve titles, but have not yet played them. Might as well wait till they come out on Linux now!
this accurately reflects current usage, Mac OSX is on approximately 7.5% of all desktops, while Linux is on approximately 1.5%. It is neither "probable" that Steam would provide more support to Linux than it does to OSX, nor would it be "common sense" for them to do so.
Since I run Linux full-time, I'd appreciate it greatly if Steam supported Linux more than any other platform, but I don't use my own personal wishes as a basis for forecasting what they will actually do.
You have to admit that if you consider Linux's market share, before a few months ago, the reality of Steam coming to Linux at all was improbable and against common sense. Yet, here they are doing it. With the attitude they're currently displaying, it wouldn't surprise me if they continue doing the improbable. Hopefully, they're rashness won't bite them in the butt until they've put out a bunch of good games for Linux.
Today you are You, that is truer than true. There is no one alive who is Youer than You. - Dr. Seuss
Don't forget about Steam Greenlight. Greenlight and Steam on Linux seem to be ideas that go hand in hand.
Even if Valve supports Linux 110%, porting all Source games with better performance, it still doesn't mean Steam as a whole will have anywhere near the library of available titles as the Windows version.
Valve fully supports Linux, great. What about Activision, Electronic Arts, Capcom, Konami, Rockstar or any of the other dozens of companies listed at the bottom of http://store.steampowered.com/?
If the only reason you think your software is better is because it's FOSS, you need to write better software