The main difference is in browser support: jQuery Mobile is on its way to supporting Windows Mobile, Opera Mobile, and almost any new mobile browser while jQtouch is only for Webkit. Also, jQuery Mobile works pretty well in Google Chrome from my experience if you're inclined to use a mobile app on the desktop for some reason, while jQtouch doesn't have animations on Google Chrome.
EDIT: And it's officially supported, meaning it's here to stay.