I understand where you're coming from, but I think just about the opposite.
Pro level cameras should be even bigger, because it is actually that, a camera meant to be used on professional assignments.
I'm serious on that bigger camera talk.
Heavier cameras balance better with heavy lenses, and most of the time, one SB-900 on camera.
Try that with a mirrorless, or DX entry level cam and see how it goes...
Another important thing to consider: pro cameras are often used on assignments where people are all around.
People think big = serious, and the professional market is dying in such a fashion, that you gotta have something to set you apart from uncle Joe.
To illustrate my point, take a look at an Arri Alexa rig ready to shoot, and see how big it gets.
It leaves no doubt how serious it is. At least way more than Bob and his GH2.
The same way an Alexa means business right from its looks, the same should go for pro level DSLRs.
My 2 cents.