Does the Scala version that sbt uses to run matters? Can it be changed?
p.s. I'm not asking about changing the Scala version against which your project is build.
In regards to the current version, looking at the changelogs for sbt, there are several updates that mention a new version of scala, the most recent of which is:
Scala version is bumped to 2.10.5. [...]
As for changing it, I don't believe that's possible, unless you want to build it (and any plugins you are using) from source yourself.
Does it really matter? Not really! Your project itself will use whatever version of scala you specify. There are only two ways I can see that it might matter - if you want to write a custom sbt plugin to us in your project that relies on a feature of a newer scala version, or if you want to use one of those features in your build build files (which are just scala scripts). However, I really can't imagine what you would need to do for a build that you couldn't accomplish with the features of 2.10.x.