Because in order to have no problem surfing using ipv6 you would need a router that supports it. Basically it's not just switching a switch at isp and all is good.
You don't need a router with v6 anymore than you don't need a router for v4. But even that is a lame ass excuse. Every current router from D-Link/Linksys/Netgear and Apple support it and most of them are not even really all that new either.
