I think you're right.
Early on git got a lot of traction, and I think this was largely due to github being so, so good.
Since the acquisition, bitbucket has come a long way in a short space of time, and I'm sure they're clawing back some marketshare. Now that they have forking, pull requests and git repos, there's no reason not to use them.
For some reason though, I still find it easier to browse / read / review code on github.
People like to bitch about git's command-line interface. But most of the quirks have been ironed out over time. What you're left with is a very UNIX-y program. If you understand the concepts then you will figure it out. git also has pretty good Windows support now, thanks to the GitHub client and others.
I don't know much about Github versus BitBucket (or any other site.) I use GitHub because we use it at work and because I found it first. BitBucket now supports git repos, which might make it a contender. I get the feeling that you're more likely to get contributors if you start on GitHub, simply because people are more familiar with the site's interface. But nothing I put on Github has become mega-popular at this point, so I don't know.