Yeah, these things are mostly true (apart from git, which I think has the best possible interface for a VCS), but I don't understand why did you suddenly switch from a question about a decision by a particular company to a question of wide adoption of technology by a community.

And your second paragraph misses the point: it's not about one of the factors, it's about balance between them. In this particular case, the amount of users who prefer XMPP doesn't seem to be big enough to counter the pain of supporting it.