I think I have it figured out, but I'm not sure. Nick at Nite can't afford to air them because shows like, The Cosby Show are really expensive, because I heard that Bill Cosby makes sure he and the other cast members get big checks all the time. same with Fresh Prince, because of Will Smith's name he most likely gets a hefty check. and when the production companies lease these shows the cost of the contract is expensive because the residual checks. shows like Friends, Frasier and others all have huge residual checks causing the contracts to skyrocket. so thats why some of our favorite shows don't air, the stations can't afford it to buy them or they have to cut them off quick. it also explains why shows are on 3 and 4 channels in certain areas, they have to be on a lot to pay the checks. Nick at Nite just opts to air them because they are more modern