During the commitment phase, I understand why you can no longer vote on questions, but what about all the other stuff a site needs before the beta period can begin? Things such as: a site name, a few moderators, a domain name, a logo, etc.
My suggestion is to allow users to vote on these issues during the commitment phase so that once the Beta phase is reached, everything is good to go.
This would also solve this issue:
Yeah, it's a real mood killer to see a proposal see more and more activity, and then suddenly go dark... – Ether
... by encouraging collaboration/discussions even during the commitment phase.