Olivia: itunes- Pop vs Rock

So I've been on an itunes shopping spree today... bought a few records, Katy Perry, Gavin DeGraw... But I DO have 1 question for the kids at itunes...

WHAT IS THE DIFFERENCE BETWEEN POP and ROCK? besides the fact that Pop is sang by a girl, and Rock a boy...

So I notice that they put Gavin (whom I LOVE by the way. A REAL artist.. recorded his own lead vocals, back up vocals, Guitar, AND piano... LOVE HIM) according to itunes, he is in the ROCK category. Then I thought of a woman that's just as rock as Gavin... what about... PINK? She's pretty rock right? No. itunes deemed her POP... KT Tunstall (ALSO amazing, 1 of those hot girls that actually write her own stuff and play her own music), nope... not rock enough... she is ALSO Pop... WHY IS THAT??

I'm just having a hard time understanding what they base the "rock" and "pop" genre on. So I did more research... found that Yoko Ono is Rock! Only because she did stuff with John Lennon though... kept looking for a woman that's considered Rock... Kept looking... found ONE good 1. 4 Non Blondes (Linda Perry is probably 1 of the most talented women in the music industry), they're Rock. That's good. But apperently, itunes feel that there needs to be 4 women for it to be rock... so I kept researching and when I went onto the itunes "ROCK" homepage... all boys... even Trans-Siberian Orchestra is considered Rock... but nope... top 50: no women...

I guess Pop isn't a bad thing... There are plenty of talented Pop artists... but I don't understand why there isn't any women in the rock genre... I think that KT Tunstall should be concidered a rocker... more then Gavin DeGraw, don't you think? But when I think of Pop, it just makes me think of terrible out-there-to-make-money-music... the Ashlee Simpsons and Britney Spears out there that doesn't really need any musical talent... just the Kim from Real housewives of the world that thinks they can sing... I guess they are the people that gave "POP" a bad name...

Anyway... the point of my rant... Girls can be "ROCK"!!