I don't think Versionpress and Revisr are exactly comparable. Revisr doesn't seem like more than a Git GUI for Wordpress, from what I could tell. The database tracking simply does a sql dump. Versionpress is (at least suggesting on their site) that they will be offering true database to version control ability. I'm excited to see how Versionpress turns out.

As for Gitium, a friend just showed this to me. It does seem like a good idea for when you've developed a site for a client but then basically just "hand it over". Come back 6 months or a year later and you'll have no idea what's changed. With Gitium you could create a new branch for production and have everything tracked. Seems like a great idea.