With Mercurial, you can either use queues and the "qref" command to continually prep a commit in progress, or use the "record" extension (like an interactive Git commit) to pick and choose parts of the working tree to commit.

I suppose it's a matter of what the common case is. For me, the majority of my commits are either one or two files, or the whole working tree -- so Mercurial's defaults make sense with that usage pattern. Of course, other usage patterns would dictate more of a "massage the commit" style.