"Granted that's mostly to do with their CSS files."

I think that will be the #1 contributor to jQuery Mobile's inevitable success. It is just so easy to get working prototypes without having to mess with CSS or anything. Everything is taken care of for you, in a very convention-over-configuration way.

I recently built a mobile version of a HUGE web app in 2 days using jQuery mobile. Compared to the earlier mobile prototypes using jQTouch and Sencha Touch that took a month+.