Handz,
Sorry to break it to you, but your assumption is easily checked because the CDC and NHTSA track motorcycle crashes. Let's have a look.
4,612 riders died in 2011, which is a 2% increase over 2010, but once you subtract off road bikes, quads, minibikes, mopeds and scooters you are left with 4,323 motorcycle fatalities. However, the number of registered motorcycles increased 5% over the same time period.
Injuries were down from 82,000 to 81,000 over that period.
40% of all fatalities were the result of a collision with another vehicle - 2,449 incidents. That means 60% of all fatalities were single-vehicle crashes only involving the rider - not exactly "most".
Only 6% of those fatal incidents were the motorcycle being hit from behind.
More than 42% (1,998) of motorcyclists in 2011 were killed in two vehicle accident and 38% (757) of these were the result of another vehicle turning left in front of the motorcycle that was either going straight, passing or overtaking another vehicle.
Of all motorcycle deaths in 2011, 35% (1,614) were the direct result of the rider speeding.
Riders of bikes with 501-1000cc engines accounted for 39% of all 2011 fatalities and also represented the highest increase of overall fatalities (25%) from when NHTSA first started recording this information in 2002. (so if you were really concerned about stats you would get a 500cc or smaller)
Drinking and riding is a significant problem with Texas and Florida leading the nation in drunk motorcycle fatalities. There are a bunch of different stats on this, but essentially, a crap ton of these fatalities and injuries are the result of impaired riding - about 42% of single-vehicle crashes and 33% overall.
40% of fatalities were cases without a helmet.
The most common type of multivehicle crash is a car making a left turn in front of the rider. With vigilance and defensive riding this is an avoidable crash most of the time. By the way, we call this a SMIDSY (Sorry Mate, I Didn't See You). Don't speed in areas where there are driveways and cross streets is a good place to start.
The next is a single vehicle crash due to road surface conditions, such as gravel, water, sand, etc. Don't ride on the edge of control, a good place to be is at 70% or less of your ability, this gives you an "oh shit" safety net if something goes wonky.
The next most common is simply overcooking a corner - some of these may overlap with the previous entry because a road surface condition on a blind corner may appear to be entering the corner too quickly. Well, you did enter too quickly if you can't react to changing conditions.
Car changes lanes into you. Don't hang out in blind spots, have escape routs and emergency maneuvers planned.
Car hits you from behind. Really we are talking tiny probabilities of a serious crash here, only 6% and in California you are at almost no risk if you are lane-sharing. Lane sharing gets you out of the "sandwich zone" between bumpers - so California is actually slightly safer in this regard. Also, if you are slowing down by rolling off the throttle, give your brake a couple of taps to flash your brake light. Bikes tend to engine-brake far better than cars - even those with a manual transmission.
The next is motorcycle-on-motorcycle carnage. Don't ride with asshats.
Locked your front brake. Learn to use your brakes.
Car door opened on you. Don't ride next to parked cars. Also because this is the area where people step out from between cars to get in or jaywalk.
Going down due to weather. Run good tires, know how to ride in the wet (especially on LA's roads where everyone loses their goddamned minds when it rains and the roads get greasy).
As you can see - only a few of these involve other vehicles, and the SMIDSY is the most common and easily addressed by rider ability and awareness. I've lost track of how many times I've had a near-SMIDSY, but because I was paying attention and riding defensively I was always able to avoid it. Cars are a hazard, but the part that is the most hazardous on any motorcycle is the nut that connects the bars to the saddle.