Comment 6 for bug 600808

Tk 8.4 does not support antialiasing. The code simply does not exist. Maybe on your laptop, you manually modified the /usr/bin/wish-default symlink, or installed a backported version of tk, or modified /usr/lib/git-core/git-gui, or added a wish binary earlier in your $PATH, or any number of other unsupported things that would have caused Tk 8.5 to be used instead. (If you want to figure out why, try running commands like ‘which wish’, ‘readlink -f /usr/bin/wish’, and ‘strace -f -e execve git gui’.)

Have you tried configuring it with update-alternatives, or not? Right now, this is the _only_ supported way to make git-gui use antialiased fonts, and that will not change until the default version of Tk is bumped to 8.5 in Ubuntu.