I'm in the market for a new bike and I've noticed that a lot of companies are making purpose built commuter bikes now. Bikes like the Jamis 3, Breezer uptown, and the novara fusion. All these bikes look pretty interesting to me but it seems that pretty much no bike shops carry these bikes in my town. They all can order them but I need to test ride before I buy something.

Which leads me to my question. What makes these bikes any different than taking an old mtb frame. Throwing on a tall stem, some swept back bars, a rack, fenders, and maybe a brooks b-17. Do these bikes have very different geometry than a similar sized mountain bike? Or would this set up pretty much give me the same riding position and comfort?

I'm thinking this may be the route I will need to go as I can't get these bikes locally. I thought about getting an older Raleigh 3 speed but they are rare down here, and I can't stand a bike with weak hard to adjust brakes.