It has to do with how the 3G Protocol works. Bandwidth is not shared evenly on a Tower as opposed to Wimax which works like a traditional wired connection in many regards.
For those that care:
http://en.wikipedia.org/wiki/Wimax
Have a look at how the IEEE 802.16 Protocol it uses differs from the IEEE 802.11 used by normal wireless.
For those that care:
http://en.wikipedia.org/wiki/Wimax
Have a look at how the IEEE 802.16 Protocol it uses differs from the IEEE 802.11 used by normal wireless.