My only street crash wasn't exactly my fault, but was because of who I was riding with which you can control. A guy was doing a wheelie behind me, and looped it as he came past me, his bike ended up in front of mine before I could do anything and I launched over it and went over the front, I had on excellent gear and only injury was breaking my rotator cuff in my shoulder, doctor said no riding for a few months but less than a week later I was taking off the sling to ride a friend's bike. It hurt but it wasn't like unbelievble pain or anything but there was a moment when I was laying on the pavement that I thought of what if it had been worse and questioned if this is what I wanted to do or not, but that went away quickly. I've crashed on the race track but again that was no big deal, no injuries I was back riding the following session.

Its generally true that if you ride long enough you will have a crash of some sort, it doesn't have to be true, but most of the time it is, if you ride long enough you will probably make a mistake at some point. You might really respect the bike and be careful but you will most likely eventually start pushing the limits. Or maybe you'll ride your entire life and never have an accident, its impossible to say when, where, why, or how it will happen and how severe it will be, but not pushing it, riding the right bike for you, and wearing full good quality gear can certainly put the odds in your favor of not having an accident, and if you do that it will be minor.

I would say to answer your question more directly, most people that ride sensibly don't have a serious accident, the majority of people that get into serious accidents are trying to ride too fast of bikes, are riding beyond their limits, or aren't wearing gear and therefor a minor incident becomes a very painful one. But if you ride smart, and start on a decent bike, then no a serious crash isn't really something you can expect on having to experience as a rider. Sure anything can happen to anyone, but that rule applies to your in the car as well .