Exactly.Thats why groups like NWA are ground breaking and people like Common and Mos Def will be forgotten the day they leave the rap buisiness.In fact,Id be willing to bet the average rap fan couldnt name an album by Mos Def or Common,but ask them if they know STRAIGHT OUTTA COMPTON.Thats why tupac and Biggie are legends and Mos Def is a nobody.
Actually, Common and Mos Def are both actors and movie stars (the former, starring in the recently-released movie, "Just Wright", a romantic comedy, in which he plays a basketball player). Plus, Common hasn't exactly left hip-hop (he's been around for over 20 years). It was just a year and half ago, he released an album, "Universal Mind Control", with a smash hit of the same title.
And, as far as message rap goes, it appears you've forgotten about groups like Public Enemy. Not to mention the laundry list of hip-hop icons (Will Smith, MC Hammer, LL Cool J, Heavy D, etc.), who rose to prominence, sans the cap-bustin', calling-women-"b*%&#), and yakking on end about money.