Is the RT6570 the "World Mode" chip that the Qualcomm CEO discussed previously ?

As far as the wikipedia link ,a cursory reading reveals that both 802.16e and 802.20 have similar limitations as is demonstrated in the conclusion of that article.
"Since the evolution of core air-link technologies has approached the practical limits imposed by Shannon's Theorem, the evolution of wireless has embarked on pursuit of the 3X to 10X+ greater bandwidth and network efficiency gains that are expected by advances in the spatial and smart wireless broadband networking technologies. What will clearly define 4G more than either WCDMA or OFDMA wireless link methods will be wireless networks that more effectively adapt to and take advantage of available spectrum."

Could the 700MHz spectrum be that spectrum required for 4G implementation to begin to be practical ?

http://en.wikipedia.org/wiki/Wimax#802.16e
Look at the table along the right side. WiMAX is a "Pre-4G" technology. The reason...
3G networks are telephone networks with data access methods slapped onto them. WiMAX IS ONLY a data network, and if you want voice, you use a VOIP application. The reason it would cost so much is that it is a completely different way of thinking about the network.