What limits wireless bandwidth?

Proprietary high-speed WLANs use variations on these standard techniques to provide higher bandwidth, either by changing the way data is transmitted or by bonding together more than one channel.

Note that data rates are not the same as throughput. Data rates represent the speed at which frames are transmitted/received. But those frames include data, control and management traffic, as well as errored frames and "dead air" when no frames are waiting to be sent. As a result, application throughput is much lower than the negotiated data rate.