Not sure if you're asking about the speaker choice or the layout choice so here's the answer to both: I was redoing a 5.1 setup having decided that I no longer wanted surrounds because of the hassle of running cables. I move too much so until I have a dedicated room I'm not bothering with rears.
As for the speakers, it seemed when I researched that using a single R3 as a center channel was better quality than using the R2c for less money. It just performs better overall, so I split the purchase of a pair with another forum member and that's what we did.