Apologies, this is what I get for not drinking coffee before commenting. You're completely right about keeping state when it comes to models.
What I don't see - and again, I have not dived very deeply into the router; I'm going off the documentation here - is how to keep views during the transition. In my app, the router has to re-render all views when changing between routes. This isn't a huge deal, as it's a very lightweight application. Still, Backbone offers much more flexibility when it comes to views.
