I'd be interested to know how similar the two apps (iPad/iPhone) are from a coding perspective. Does it make your job as a developer easier or harder to create a single app that works on both? It seems like it would be a little more complicated initially to add the media queries to determine what device it's on, but would make your job easier in the long run to only update a single app.
....Unless of course that would cause Marvin to lose functionality...that would be really BAAAAD! lol