Voting has its own risks. After all, democracy is the original 51% attack, as Erik Voorhees puts it so nicely. Before you know it, we might have Bitcoin taxes. Still, it's possible some less drastic dispute resolution mechanism than forking Bitcoin or switching to a rival currency will emerge. It's certainly interesting to speculate about the possibilities.
The thing is we already have one voting mechanism, mining. But that is a mechanism where the right to vote is dependent on your access to highly specialized hardware and in practice has been held in the hands of a very few in Bitcoin's history due to the natural incentives for miners to mine at large pools.
By adding proof-of-stake voting you counter-balance that vote with one where access is determined by a resource that all Bitcoin users have, Bitcoins themselves. Obviously we can't force miners to make larger blocks, but we can make it clear what maximum size we will accept, so the two voting processes go hand-in-hand.
As you say, it's a dispute resolution mechanism.