Yeah, it is true - personally I see them as different genres, not two sides of the same coin. "Contemp R&B" is just urban pop: the mellow, laid-back beats of hiphop infused with a dose of lame pop divaship, or worse, the likes of Akon, T-Pain and Ne-Yo.
If one played some old rhythm and blues to a bunch of kiRAB exposed only to urban contemp, they'd have no idea that they were listening to something that was also once termed "rhythm and blues". This to me shows that attempts to group them under a single urabrella are dubious, tenuous at best. Hell, modern r&b listeners don't even RESPECT old r&b. I've never come across an urban contemp station willing to play, every now and then, a 60s/70s r&b track. That's because they realize it just doesn't fit in with their sound at all. Modern rock stations by contrast will always be happy to play an old classic here and there.