As far as the userspace configurations, that is definitely a concern. I'm guessing that Steam will probably ship with a pre-packaged set of libs that games can easily use, so that they don't have to worry about the particulars of specific distros. That's not exactly the linux way, but it does seem like a fair trade-off, since the LSB hasn't been able to fix that issue.
I also expect they will only officially support a few distros - Ubuntu, with maybe a few others sprinkled in, and then just be friendly towards allowing people to get it up and running elsewhere, without providing any real support for them. Plenty of linux apps run fine cross-distro without going to any great lengths.