I haven't looked closely at them, but Marketo has a
responsive emails category on their templates site. Would be interesting to see how theirs are built, and what doesn't get changed in theirs, as opposed to what's happening to yours.
I've built a few simple templates with the
Zurb Ink framework, and haven't seen many major issues yet - not to say I wont though. Also, I vaguely remember reading that was the same framework that Marketo was basing theirs on?