I think the death of R&B can be attributed to two things:
1) The same thing that's killing hip hop, when we started letting these old white (and not even necessarily white) CEO types dictate what gets put out because they're only in the business of selling records. Who cares about artist integrity? Sound like the next guy because he sold X amount of records.
2) Singers no longer are brought up in the church. I'm not a super religious person, nor do I care what a lot of these "brought up in the church" singers did in their spare time, but one thing that can't be denied is that it honed their skills. Church singers also have to sing with feeling, thus birthing that "soulful" sound.
1. Nothing is really killing Hip Hop in 2012.
C.E.O's see that funding a Hip Hop project in 2012 that isn't good music is failing.
This isn't 2001-2005/6, you can't just go platinum off of a hot song.
A lot of cats that are currently hot grinded their way to their spot.
Meek Mill, Wale, Kendrick Lamar, J. Cole, Drake, B.o.B. all put in extensive work to get to the point where they can sell hundreds of thousands of records, all while staying "Artists" and not carbon copies of each other.
The Chief Keef's, Waka Flocka's etc. will come and go but cats like these dudes will have much longe careers.
It's the reason we see Kreayshawn's 5,000 records sold against Kendricks 326,000 or Drakes Platinum Albums, or Lupe's 100,000 records sold.
The problem with R&B at least with Black artists as far as I can tell is the genre has no real community or culture to it.
R&B artists are separate from each other, the Community/Culture of Hip Hop is what differentiates Hip Hop from R&B
and most likely is what ultimately lead to R&B being consumed by Hip Hop.
In Hip Hop collaborations are common and not wanting to be left behind a lot of R&B artists started using Hip Hop production Techniques like sampling, then they copied whole song structures and eventually they created music over the same instrumentals choosing Hip Hop producers over R&B producers who happened to make a little Hip Hop.
On top of that these kids with singing talent are growing up in the same communities as the kids with rapping talent and a lot of would be singers most likely became rappers or producers and engrossed in Hip Hop culture, that isn't to say there aren't singers out because I'm certain there is plenty.
I don't know the entire 60+ year of R&B but I think I can say that the last 30 years are pretty telling of what's happened.
2. You don't need the church to develop a soulful sound and honing your skills can be done in entirely different settings. Taking college courses, home training courses or getting a decent singing coach/teacher (along with a great deal of talent...) would enable mediocre singers to hone their skill and become great, while the exceptional ones would leave their peers behind.
With that said I don't think R&B Died there is some really good talent out there. I just feel that a lot of the people who say "R&B Is dead" are also in the same crowd of people who don't actively follow any new artists in Hip Hop.