I don't necessarily think that the R&B genre is "dying", per se, but I believe it's decline is a product of two things:
1.) There is a demand for crossover appeal. Instead of sticking to one genre, you now have a multitude of artists trying to experiment and clash together characteristics of certain genres into one. Contemporary R&B has started to embrace elements of the ever-so-popular electronic genre, which has been "the" genre for the past few years now. Which brings me to my next point.
2.) It is in a transition. R&B has enjoyed decades of mainstream success up until recently, and I believe that it's just a natural cycle. What's hot now will not be hot in 20 years.
I never found Usher to be that great of a musician to begin with. He's a fabulous performer, but his discography is a mixed bag. I definitely prefer listening to his singles rather than a whole album.
It kind of irritates me how the likes of Usher, Beyonce, Rihanna, Chris Brown, and Ne-Yo, have all transitioned into making those techno-pop club songs.