They want to keep there network core switch where there full network will be connected by 10 gig
Nexus, by design, is aimed at DC networking and you can't substitute Nexus with a 6500.
Current 6500 can handle a few 10 gbps links. But if you want something that can handle 40-, 100 Gbps, then you need something else. The 6500 will be getting a new addition to the family. The announcement will be made, possibly, during Cisco Live Orlando 2013.