> Except that if you added a new file then "git commit -a" will miss it out.
Exactly like Mercurial, you mean? Try it if you haven't in a while: you have to call “hg add” to add a new file or you'll get “nothing changed” when you run "hg commit".
The reason why neither of them has a default “add everything in the current directory” mode is that this is how you end up with repositories containing temporary files, build artifacts, and secrets.
This is not a good example to base ”much better UI” claims on.
Git's UI is full of little sharp edges like that. You get used to them, but it's just needlessly fiddly to start with.