> But you can do broken commits just as easily with svn - I've seen people commit all changed files, forgetting to add a new file and making an unworking commit.

If you do that, you've made a mistake. No tool can save you from all mistakes (though they can help you out with warning messages and such).

Partially-staging a commit in Git is doing the same thing on purpose. It's functionality that explicitly helps you make this mistake.