People are also making the easy assumption that what's played on the radio and seen on BET/MTV is representative of EVERYTHING crafted musically in hip-hop. What music you do observe likely has a big promotional machine behind it (locally, regionally, and nationally, by the labels).
It's been mainstreamed by the mere fact it's in the public eye/ear. It represents a significant chunk of what's being done. But by no means is it the whole pie. You've heard of 50 Cent, Ludacris, and Snoop Dogg--what about Murs, Little Brother, MF Doom, The Coup, dead prez?
Here's a more telling example of how the game is played--I'm sure that someone here has heard of The Roots. (You've definitely seen their Afro-ed drummer '?uestlove' on TV commercials.) The hip-hop band has toured and performed to sold out shows for years. But I'll bet you can't remember the last time you've heard them on the radio. And they've only been recording for about 15 years.
Gosh forbid that anyone think that country music begins and ends with Tim McGraw, Faith Hill, Toby Keith, George Strait, or Alan Jackson. It has WAY more depth than "Hawkey* Tonk Badonkadonk" or "Country Boys and Girls Gettin' Down on the Farm". :
Getting back to my original thoughts--there's PLENTY of hip-hop acts and music to choose from. Radio only plays what makes them the most profit--i.e., listeners to numb with advertising. Rapper David Banner was right--our society loves the sex and violence and the vulgarity, and to try to pass it off as just a 'rap problem' is convenient and short-sighted.
*spelled as such due to language filter