It matters a lot if you're using open source tools, I think.
The people running windows and doing development on open source tools are a tiny minority, therefore whatever platform specific problems they run into aren't going to get as much love and care.
It's different if you're using some proprietary soup-to-nuts toolchain, perhaps with support and all that jazz, then maybe it doesn't matter.
But as long as your support is the open source community, and your tools are the stuff that they put together, and as long as they're all running some flavor of unix or linux (and therefore don't really care about your weirdo windows vista edge case), it'll matter.
The people running windows and doing development on open source tools are a tiny minority, therefore whatever platform specific problems they run into aren't going to get as much love and care.
It's different if you're using some proprietary soup-to-nuts toolchain, perhaps with support and all that jazz, then maybe it doesn't matter.
But as long as your support is the open source community, and your tools are the stuff that they put together, and as long as they're all running some flavor of unix or linux (and therefore don't really care about your weirdo windows vista edge case), it'll matter.