From what my customers say, first time commuters, especially those who haven't ridden a bike in years, do seek mental comfort, a bike that will make the transition as easy as possible. Others who choose them do so because of image. Not necessarily the image of commuter bikes, but the image of road or mountain bikes. They see roadies all crouched down in the drops, and don't want to put their body through that. They see the image of mountain bikes as extreme "dudes" blasting down the side of a cliff. They know they aren't interested in doing either, so a commuter or hybrid bike feels like a more reasonable choice.
Many commuters who have owned a road or mountain bike already know how their body is positioned on those bikes, and prefer a more upright position of the commuter bikes. The want the commutes to be a break from the bent back and tilted neck. The roadies enjoy the ability to use wider tires, more cushion. Mountain bikers would rather have a dedicated commuter rather than a "compromised" mountain bike.
When someone thinks they want a mountain bike for commuting, I tell them straight off they'll be better off taking off the knobbies for tires with better rolling and no squirm. So they figure they might as well get a commuter bike that comes stock with right tires rather than pay for a mountain bike, then pay for different tires. Most of the road bikes we sell cost much more than the commuter bikes, so people avoid spending that kind of cash unless they know they'll be doing group, training, or charity rides, or racing.

It never occurred to me that having one kind of a bike or another would make any difference to the ability/need to concentrate on what you're doing on the road. I don't see the connection personally.

A folding bike makes multimodal commuting more practical, if the country you live in
made the investment to make their part of the system work..

bike train bus bike..

ItsJustMe-

When riding on the edge of the paved road, and cars and trucks start flying by at 50 mph, and there's no shoulder except a drop-off of 6 inches into gravel, broken glass and/or trees, I tend to tense up a little. I have essentially 6-10 inches of room for error. There's no "taking the lane " on some parts of my commute, and 23 or even 25 tires don't deal well with slipping off the road at that point.:twitchy:

And the rumble strips on the shoulder every few feet to let the cars know they're running off the road don't ride too smoothly on 23's and aluminum (or even carbon) frame. When it's already a 2 hour commute, you can't always change routes that easily and lengthen the ride.:(

I'd still rather ride than drive when I can though.:)