As mentioned in lots of other comments, Linux users go to their package manager -- an App Store that runs 100% off promotions 24/7.
Mac users have an App Store now.
Windows users are still using SourceForge.
Actually, I expect that Mac users are overrepresented: every time you go "brew install blah" there's a good chance you're downloading off of SourceForge.
Surprisingly,
since 11/1/10, windows has less downloads than all others combined.
Since 3/1/11, windows + mac + linux have less downloads than other alone.