Again, I can't find the man page I took it from, but when I type "git config --list" and "git config --list --local" git-bash[1] gives me different results. The latter prints out content of the repo configuration, while the former shows system, global and local configs combined (in that order). In other words --local gives the same result as --file .git/config. In my setup, omitting --global and --system works differently from what you said.

[1] 1.7.4.msysgit.0