First, Michael Cole is awful. There's no way around that. Smackdown's commentary works because of JBL and his aggressive heel personality.
I agree with what people said earlier... as soon as King became a 'face' commentator like JR, it all went to hell. I was watching some old matches the other day, and the commentary worked because each man was pulling for a different wrestler. Now, they never disagree, and that also serves to make the heels look weak. Think about some of the Smackdown heels... Finlay, MVP, Edge... they're a lot more over because JBL spends EVERY match building them up.
How often does Orton get complimentary commentary? If the announcers don't believe in someone, how can the viewer? You need a heel/face duo announcing so the fans have a voice representing them on TV no matter who they support.
Problem is... King and JR wouldn't work well with anyone of the WWE's other announcers, neither would Michael Cole. Styles is good, JBL is great... they might work well together, but then that'd leave us with what? Taz and Cole again? JR and Taz? Lawler and Cole? None of the possibilities really work.
Basically, we're stuck with King and JR until they retire, or until Vince decides to fire Good Ol' JR again (which, if history holds, should happen again soon

).
Of course, the interesting question here is what happens if JBL comes back as a wrestler, which he seems to be in training to do. Have Taz cover two shows? Coach is busy, so there's a lack of people for that spot if he goes back into the ring.