Regardless of what technology they use, there are laws and regulations
that assign bandwidth and there isn't a large spectrum hole anywhere
that one can plug into without a transmitter license.
In any case, some of the wireless monitor connections _do_ use 802.11.
And they can, at significant degradation. If, for example,
you are contend with 1025x765 @ 5Hz with 8 bit color, then
you need only something like 32Mbit/sec to transfer it
lossless. But the resolution and color depth was current
something like 10 years ago and the 5Hz refresh rate
even annoys when working on a command line.
For a slide-show, however, that has very large fonts anyways
and only slow, localized movement, it is enough. But not if
you want to work, play and watch movies with the display.
What I am just saying is that a general-purpose, full
cirrent PC graphics quality solution is not available now and
is very unlikely to be available in the near future. There
are a lot of specialized solutions with specific limitations.
They all work by degrading signal quality significantly,
but in different ways.