It occurs to me that ignoring the user's selected umask could be considered a bug by some people. A package manager for a distribution should presumably ensure the correct umask during install, but if a user is doing a direct install, it seems reasonable to think they are responsible for setting the umask they want used. There is a fuzzy line here, though, because distutils is also a bit of a package manager...
Regardless, though, Ned's observation seems to indicate this is not a regression. Tomi, do you find a different behavior in 3.2?