I think the idea is just plain foolish as it ties the PHP to the interface and really, has no other functionality besides submitting a form. It is a minimalistic approach to a single person's idea of "something good".
Well I'm generally all for modularization and keeping everything seperate, but I don't really see how PHP can ever be seperate from the interface (if by interface you mean the interactive web page the user sees). I mean in many cases PHP directly generates it.
Didn't see much info on the site and I've never heard of Jquery before.