We might reason like:
- this post's reputation is too good already, I'll not vote to increase it;
- this post deserves a better reputation, I'll vote for it;
- this post's reputation is way too high, I'll vote it down.
So, altough we can't rank the posts directly, we could do so indirectly. It could also lessen the effect of the inflation which affects the reputations as new users join the community.