Yeah, Hubpress, Octopress, Jekyll Bootstrap, and at least one other I can't quite recall, are all the idea of having a preconfigured blog theme ready to go instead of having to build one from scratch (or stick with the very plain Jekyll default). They'll sometimes do things like pre-configure useful Jekyll plugins and provide additional scaffolding tools (this used to be a particularly big deal of Octopress, IIRC, for the versions of Jekyll before it added its own scaffolding system).
It's a nice to have to get started quickly when you don't want to custom build a theme or you want someone else to figure out a lot of the basic configuration.