as you say Zing if it can detect the change then it must at some hardware level support 100 WAN unless they fiddled the firmware bit flipping on another part to try and shift the old gear.
its always werth haveing a really good look on the
http://wiki.openwrt.org/TableOfHardware page as you will note that the netgear is untested or WIP(but its on there so they are reasonably sure its got the hardware so might/should run openwrt).
its been a while since i checked that page but i cant seem to find any (wireless if your thinking about that option)11n parts so far, and they will have the better WAN port and throughput etc.