What surprises me is that no left-wing equivalent of
Limbaugh has become popular cuz the Shrub certainly provides lots of
material.

Heart-string-pulling arguments (pleas to pure emotion) work better on
television, or cinema. Dry logical debate works best in print. But the
thing that works best on radio is logic, fueled by passionate belief.
That's the essence of conservative talk radio.

Also, the left already own print media and television. Radio is not an
"outlet" for liberals because their viewpoint is already prevalent across most
media.