Xara Cloud can read desktop website project files and make edits / additions to them, but I would say it's a secondary feature to its main purpose (i.e. we've not put as much development time in editing website project files as the business document editor).

I suspect Adobe has the resources to venture into that sort of market. I'd be interested to see where tablets are in the next few years, as I understand it Tablet sales have been gradually slowing recently.