If it isn't enforced by the blockchain then it should be stated clearly in the proposal. It could also be in the metadata for purposes of automated data collection on proposals, but visible in the post is important to so voters can see it and hold the proposer accountable for it.

I'd like to see this feature in the blockchain too, since there are quite a few proposals that don't make sense unless the necessary amount of funding is provided to actually accomplish the task, but of course that is more complicated and won't happen until the next hard fork at a minimum, if then. Without that, we should be able to rely on reputable proposers to send it back.