Github may be a commercial provider, but at least it's a commercial provider based on an open protocol. If things do start going wrong at Github, escape is a "git clone" and a "git push" away.
A lot of the content on Sourceforge isn't in SVN. I think some of it may still be using CVS, and a lot more is just in the "project files" catch-all.
Also, SVN is a lot more annoying to copy, especially if you want the whole history. Not that it isn't doable, but it's pretty slow and obnoxious. With Git, every clone includes everything by default.