Yeah I mean, especially if you're talking about coverage for a full frame sensor, those lenses aren't getting any smaller. The 2.8 standard zooms, the 2.8 70-200s, the super telephotos, these things don't benefit from having a smaller camera with less space to have a solid grip on. Not to mention having a flash mounted on the hot shoe. Rebels are fine, but the bigger grips on the prosumer models are more comfortable, not to mention the pros will also being using a grip for portrait shooting, making the body bigger still.
Plus, I think Canon and Nikon will be making optical TTL viewfinders for a long time, simply because that's what the pros want and are used to having. They may offer a hybrid optical/electric finder like the Fuji, but I think it'll be some time before they abandon an OVF, if ever.