The Steam store is not coming to Linux in general. It is coming, specifically, to Ubuntu. But that’s not the problem. I have no issue with Valve only supporting one Distro at launch. The problem is that Ubuntu already has a software and game store – the Ubuntu Software Center (or “Software Centre” for you crazy kids on the other side of the pond).
Now, I’m not opposed to some healthy competition. Quite the contrary. But, in this case, I’m concerned. We don’t need two software stores. We need one that is highly successful and pulls in large-enough sales volumes to attract developers and publishers to the platform.
Currently, the Ubuntu Software Center is still in its early stages. It’s growing and improving, but is not yet large enough (in terms of individuals actively using and purchasing software) to make it truly enticing for publishers to invest the resources needed to port their wares to Linux.
My chief concern is that the arrival of Steam will simply serve to splinter the already small (relatively) user base of “people on Linux who buy software through a digital store."
I would prefer to see Valve release games, starting with Left 4 Dead 2, through the Ubuntu Software Center. That would help bolster an existing effort to build a Linux software store while still giving Valve access to a new base of users.