Can't be too sure about it, but prima facie it seems that this WMM thing is not a change at the physical level (which means it is not a new addition to the b,g,a .. series). The change is most probably at the MAC level/network management level which again should not lead to buying of new equipment. Its just got to do with providing a higher priority to streaming to ensure a better QoS.

Well, most of technologies do provide a higher priorty for streaming anyways, so essentially what is unclear is how much of a higher priority is streaming being provided under WMM ?