You really hit it on the nose with tire profile! That has a bigger impact on rolling resistance than tire size. I`m testing out round profile tires only - even though some tires designed for asphalt have a square profile - similar to mtb tires in that regard.

Guess its pretty safe to say that most people have no problem understanding that mountain ike tires don`t work well in road bike competitions and roadracing tires are a disasterous choice for offroad racing, but urban commuting is a little more difficult to nail down and there I feel that tire choice should be determined by road conditions, what you`re packing and how important/unimportant an extra mph is to you.

Personally I`m finding wider tires give me more control, confidence in traffic and don`t affect my average speed to any serious extemt.