People will not shell out monies for a games console with no games as some people above have pointed out.
Gaming on the Mac is only possible via bootcamp and this is the only realistic option aside from having a dedicated gaming PC I can see for the foreseeable future. Hell, the original Half Life is not available for OSX. I intend to play it once the Black Mesa Project is finished. Don't get me started on getting surround sound out of games on OSX.
Mac games take too long to come out, cost too much, don't run as well (usually) and have significantly less modding options.
I agree with the above, Apple buying a games company as good as Valve would be bad news for everyone.