Well here's my 2 cents. I've had an '04 for almost 2 months now and have put about 600 miles on it. As BajaFool said we disassembled the idler gear/torque limiters on our bikes and compared (his is an '03). I do not believe there is any difference in the crankshaft taper or diameter all though we did not measure it. IMHO the problem with the '03's is not the woodruff key. That is just the symptom. If you look at the '03 starter drive it is clear that it cannot turn backwards. If the engine kicks back there is nowhere for the force to go except into the starter drive. Actually you are lucky if the key shears because if it doesn't something else is likely to break instead (there are some other posts describing this). In the '04 you can turn the crank backwards with no issue since it has the torque limiter which slips under those conditions. The lean jetting that the '03's came with aggravated the problem. I think if they had been jetted properly from the factory the problem still would have existed but it wouldn't have been so widespread across so many bikes. Basically it's a weak design coupled with poor jetting. I believe the '04 is a much better design and will probably prove to be very reliable. Only time will tell.
My question is that if the main crank starter gear is on a one way clutch how do we get a backfire to load up the starter motor drive pinion?