I've crashed road bicycles numerous times wearing classic bike gear and you do get scraped up, but generally you are not going 60 mph and most bicycles don't weigh 500 lbs. Bicycle riders tend to avoid heavy traffic areas even more than motorcyclists--for example I would rarely ride a bicycle in the fast lane of a divided highway or city street, unless I had to make a left turn. Frankly, road rash is the least of your concerns on a motorcycle--it won't matter if you're all scraped up if your head is squashed.
But, I get your point. The thing is everything in life is a compromise. You can never be perfectly protected, and you have to wear whatever gear allows you to operate that vehicle in a safe and enjoyable manner. Really, we should all be wearing double harnesses and full coverage helmets in our cars, and we would be significantly safer. For that matter, lots of people fall and are killed or injured in bathrooms, but I would prefer to take a shower without a helmet on.
For my part, I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to move. Robert Louis Stevenson