What do people look for in R&B and Dance Genre?

When we hear about R&B, we link Artists such as Rihanna, Ne-Yo, Usher, etc.
Dance on the other hand being artists such as Cascada, Tiesto, Inna, Katy B, etc.
However, when we look at artists who make both genres of music, together, being dancehall/r&b/, they named artists such as Usher, Rihanna, Black Eyed Peas, Lady Gaga, Justin Bieber, Loick Essien, etc.