Tagging on to DanO220's comments, I think his description of being on a motorcycle and having a car encroach on your "space" (aka, cut you off) is very typical and it doesn't matter if you're riding a pink BMW in a neon Aerostich jumpsuit or a black Harley with 120db's of exhaust note. It happened to me two nights ago and it's not at all unusual when you're in late afternoon city traffic approach intersections and some idiot in a cage decides to jump into the left lane so they don't have to slow down for traffic turning right at the light, or on the freeway as traffic begins to slow in their lane.

I would also note that your description of riding a bicycle and having a car encroach on your space is also not that unusual. The HUGE difference is, in the motorcycle scenario the motorist does a quick check of the mirror and fails to check their blind spot and litterally cuts you off while you're both rolling along in traffic at 25 - 70+ mph. The results can range from either one or both of you making a minor evasive manuever to avoid a collision to an accident from which you as the motorcyclist will lose in ugly fashion: there's a reason that first responders and troopers call it scraping 'em off the road.

In the bicycle scenario, what you usually have is a motorist who not only sees you, but who makes a conscious decision to share the lane. However, the big difference is, the latter happens as you describe it, while stopped in traffic or while taking the left lane to make a left turn. These encounters are usually more psychologically upsetting than they are physically harmful.

As for the left hook, cyclists and motorcyclists are equally at risk in this scenario. The biggest difference in terms of "danger" is the severity of the injuries that will result from the speeds involved. If you're riding on a motorcycle at 30 mph and T-bone a car that pulls out in front of you you'll fly just as far as you would on a bicycle travelling at 30 mph. If and how much protective gear you wear on the motorcycle is about the only thing that will mitigate some of the trauma from the impacts with the car, ground, and any other cars or objects that you hit (or that hit you) along during your trajectory.