There are several groups trying to navigate the issues of open source development in the developer tools hosting market, too. Sourceforge lost a lot of its early dominance due to both reliability issues (as bigger projects decided it was worth the hassle of switching to self-hosting to gain more control) and being slow in offering new version control systems (initially Subversion, later Git and Mercurial).
They're still one of the bigger open source players in the hosting game (Allura is AGPL), but the revenue models of GitHub and Atlassian actually give them an advantage here, as their free-as-in-beer tier can be focused entirely on providing an awesome user experience, without needing to worry about making room for ads.
Zero cost, an excellent user experience and the network effects of GitHub and BitBucket are too tempting for even me to resist - while it annoys me that GitHub and Atlassian reserve the right to screw their users, that's very different from believing that they would actually do so. That's another reason I find the situation so frustrating - they're reserving the right to do something I don't think the current leadership would ever do, but I can't say the same for their successors in interest, and strategic missteps have led to changes in control at far larger companies than those two (compare the way Sun handled open source projects to the way those projects have been handled by Oracle post acquisition).
In addition to Sourceforge with Allura, other open source projects like Gitorious, Gitlab, etc, serve to keep the leading proprietary providers honest. As noted in the discussion here, if you avoid the integrated issue tracker and wiki, migrating away from GitHub or BitBucket would be an inconvenience rather than a disaster (and it wouldn't be that bad for most projects, even if they did lose their tracker data).
The user network effects of GitHub have been enough to lure even some of Red Hat's upstream projects (most notably, OpenShift Origin).