If they announce Half Life 3 as an exclusive launch title for Steam OS, I think there are a lot of people who would give it a shot. Steam is a very influential and well-connected company, don't underestimate them.
It's an operating system, there are not going to be exclusive launch titles. Unless of course, you think Valve is going to release HL3 only for Linux users, but that idea is absurd.
Games run on operating systems. They revealed there are going to be some AAA titles coming to the OS. Of course if HL3 eventually is confirmed it won't be a solely Linux only release but that doesn't mean Valve won't release it for the OS though. It was an example.
