What exactly are you defining as "quality mastering"? Hip hop producers spend an excessive amount of time mastering tracks. A majority of albums are released via optical disk or 12'' just like any other genre now. Not to mention as a majority of the production is handled through programs, the sound is often more refined than other genres. Any good producer samples vinyl. I just don't understand how a "majority of hip hop" could lack quality mastering versus another genre recorded recently. Of course there is poorly mastered and recorded hip hop, but no more than any other genre.
And I don't even really like this discussion to begin with... it's about the quality of the music not the quality of the recording.
CunninLynguists - Piece of Strange (2006)
Curren$y - Pilot Talk 2 (2010)
Digable Planets - Reachin' (1993)
Foreign Exchange - Connected (2004)
Pete Philly & Perquisite - Mind.State (2005)
Q4 - Sound Surroundings (2010?)
TM Juke - Maps From The Wilderness (2003)
It is worth mentioning that I am rather biased as hip hop is home base for me in terms of knowledge and enjoyment. As I was saying, I would recommend some instrumental based hip hop.
BAHWEE, Dr. Who Dat?, Fat Jon, Nujabes, Hubert Daviz, Dela, Onra, there are tons.