There are no differences in rolling resistance between 650 and 700 tyres related to their respective sizes. Although obviously a 700c/23 Conti GP 4000 is going to roll faster than a knobbly 26" mountain bike tyre!

In my experience wheel size is pretty irrelevant on a commuter when compared to other factors, i.e. how well the bike fits, whether the contact points are ergonomically thought out, whether the bike is fit for its purpose, if it's raining etc etc.

A cheap MTB with skinny slick tyres and fenders will almost always make an ideal short to medium distance commuter. Nothing to do with the size of the wheels and tyres though, they're just good little commuter bikes - robust, reasonably unattractive to thieves, easyish to wrench, solid and dependable.

Hope this helps. I think I've successfully confused myself along the way though. What were you asking again :-)