Earlier quoted context omitted.
You are assuming a monotonically increasing version number. What happens when you need to go back to the old "version" and push out an update? For instance, you shipped 3.0 a few months back but most of your users are still on 2.7. Uh, there's a bug on 2.7, you need to push out a fix. If you are doing versions by date, then there is no easy way to distinguish parallel development.
Just to play devils advocate, you could use both versioning schemes. For example, 13.01.24 could indicate it was the 24th revision of the 13.01 release (as opposed to being released on the 24th of the month).
13.01-24
http://fedoraproject.org/wiki/Packaging:NamingGuidelines#Pac...(i can never quite distinguish between revisions and releases... when is each used?)