Dual-receiver and transmitter - Why?

I was studying some datasheets from companies that produces transmitters and receivers for Wimax/Wifi... and some of them has 2 receivers and 1 transmitter. It's not enough to have 1 receiver and 1 transmitter (or a transceiver) Why they have 2 receivers? There's any special reason for that?
Anyone could explain why?

Best regards,

Canosa

Link: http://www.beceem.com/images/BCS5350.pdf

The datasheet tells why. To implement diversity http://en.wikipedia.org/wiki/Antenna_diversity and beamforming.