From what I understand it comes down to cylinder count and also the "power band". Such as if you ride a 500cc bike V.S. a 600cc bike, there are a couple things to consider. And as stated earlier, the cylinder count. A 2 cylinder is not going to have as much pull as a 4. I ride a 500cc ninja, but my buddy has a 636. He has let me "demo" his bike, and there is a huge difference. On his bike (a 4 cylinder), everything happens... quicker... if you will. That and when I come out of a turn on my bike, I have to really put on the gas, on his, a flick of the wrist and I am gone. And when I say the power band. My bikes power band kicks in at around 5.5k, and caps at like 7.5k. So within that range is when I am pulling (dont get me wrong, the bike will still accelerate, but between those two points is when I can really feel the juice). And if I remember correctly, his is between 5k, and goes all the way up to like 12k or 13k. Thats a HUGE difference. So in between those two RPM counts, your bike is so-called "pulling". So Imagine if you accidentally come out of the corner with to much heat and give it a little gas by mistake. On my bike, its more "forgiving" in the sense that it has a shorter power band so if I do make that mistake (I have), then it probably wont cost me as dearly as if I did it on my friends 636. On his bike, if you did that, then the bike is going to jump from lets say 55mph, to 70mph in a blink. And if your a newbie and don't know what to do, then bad shit happens. Its happened to me, so I speak somewhat from experience.
So back to the point, when they say forgiving, they are saying that you can get away with more things on a smaller bike than you can on a bigger bike. That's why a lot of the more seasoned riders say start off with a "smaller" bike so you can get used to throttle control, and also clutch control (and other things as well). Think of it like this; Image you have never flown an aircraft, Would you start off with a trainer, or would you start off with a F-35 Raptor (latest and greatest in our militarizes jets)? So after all of those examples, I think that it can help to explain what it means to have a more "forgiving" motorcycle.
- Ghost