I am considering a Canon 70D for motorcycle touring. Considering the vibrations that a motorcycle will put the camera through, is this a good choice? Are the vibrations a legitimate concern?
I wouldn't be concerned much about the camera body; there isn't really anything in it that would be very sensitive to vibrations. The only mechanical parts are the shutter and mirror, and both are in a safe postion when the camera is switched off.
Lenses are a different matter: individual lens elements can and do become decentered, which can result in drastically reduced optical performance. And strong vibrations certainly could cause elements to become decentered (though the more typical cause is a single hard impact, i.e. dropping the lens).
To reduce the forces that the lenses are exposed to, you want thick and tight padding, ideally around each individual lens If you have more than one.
And, quelle surprise, that's exactly what good camera bags provide:
So if you don't have a good camera bag, get one, use it, and if you're still concerned, put some additional padding around the bag (or wear it on your back, that would isolate it from most vibrations as well).
I travelled around London on a daily basis with my Nikon D100 and a pair of lenses by bike for several years and experienced no bad effects. A suitable bag and securing it safely to the bike or on your back should be sufficient. I've also carried several laptops like this and they're much more vulnerable.
Note that I wasn't riding a hardtail chop though...
Lots of motorcycle miles on my Nikon D90 with no ill effects at all. I have camera and one additional lens in a backpack designed for a camera system which has excellent padding. I put that in the top case behind the seat or in one of the side cases (panniers). I wouldn't be too concerned depending upon terrain of course. If you're off-roading, or riding considerable distances on unimproved roads, improve your photo equipment padding appropriately.