Well, technically speaking all contemporary music be it Jazz, or Rock etc.. was derived from an earlier form of music...
and well- the thing 'no simple' jazz pieces is a little absurd... Jazz is usually improvised- You can do what ever the hell you want, inside a boundary... Its your own thing.. do however complicated OR easy as you like- where as Rock i must say is generally rather basic- always (usually) Quite simple, I haven't come across an extremley 'Hard' rock piece of music.
That said .. osakrthestudents argument is invalid. Stupid really to have that view, Yesh i prefer Jazz to most rock BUT what you're saying makes really no sense.
Rock was derived from the 12 bar blues... But hey... Jazz was derived from the classical/ modern era..
and with the Complexities 'Syncopation, Difficult harmon, talent in genral' Comment thats going no where either. Jazz can have a degree of complexity, and it may also not have... Jazz is based on improv.. if you don't get that, you don't understand the jazz concept very well..
STOP genralising the music... music is all different.. you can't compare two different 'eras' of music like that... its just... it doesn't work lol ^^
*cough* i was bored , hence the reply ^^