Anyone who has tried to cycle with a 10kg pack on their back will know that it is just a very unpleasant way to ruin a bike ride, whereas it is quite feasible to cover very long distances on the road with a correctly laden bike. One of the beauties of cycling with a load compared to hiking, is that the bike will take the weight. All you have to do is propel it!
I've done a few long road trips in my time, and agree entirely with the above quote. Even the weight of an SLR and lens in a backpack would get very uncomfortable after a day in the saddle. I used to carry a Canon D60, 2 or 3 lenses, and sometime a carbon fibre tripod in ordinary rear pannier bags mounted on the back of a road bike. I also carried a small laptop for storing my photos, spare clothing, and a few other odds and ends.
The weight was easy to deal with - a more serious problem was that I'd want to stop and take some photos when I saw anything interesting, which slowed my progress. I stored the camera and lenses in ordinary soft padded cases, which seemed to protect them just fine. For what it's worth, I had one (fairly minor) crash with my equipment aboard, and nothing was damaged. Probably nothing would keep your gear safe in a serious crash, but the same thing could be said about the cyclist too.