sorry for the long winded respose but it appears many people do not realise why they can shift without the clutch.
the ability to clutchless shift has nothing to do with the clutch, but rather the transmission itself. more specifically as to how each gear engages.
you cannot compare it to your average car either.
a normal car uses a syncronised or 'syncromesh' transmission which uses the friction of a bronze ring to match the speeds of internal parts as you shift.
a motorcyle uses a dog clutch type transmission. this type allows engagemant of gears at mismatched speeds and is what permits you to shift whithout the clutch. the downside to this type of transmission is that it does cause signifigant shockloading of the drivetrain as you shift, which is bad, but is inharent with this type of transmission. many things have been enginered around this.
first off the rotating inertia of a motorcycle engine is relatively quite low. our transmission has straight cut gears which are stronger than helical cut gears like you would find in your car. we also use a sequential shifter, making it impossible to skip gears and and have extremely mismatched internal speeds. the chain and the rubber block in the rear hub act as a big shock absorber to reduce stress.
a motorcyle like ours has been engineered to be able to shift without the clutch. no doubt doing so causes more stress to the parts and the mfg. probably doesnt recomend doing so, but given the track record of modern motorcycles, they seem to do it reliably.
using excessive force on the shifter, and changing gears while under high power is very bad though. a blip of the throttle and light pressure on the shifter is all that is needed.