Most AM stations cannot be received well in any large office or retail
facility. That is why streaming will be increasingly important.

Also, if you look at the power that some stations have in some metro
areas, and the other technical factors, both AM and FM, then it will
make even more sense.

KFWB is 5kw-U, KNX is 50kw-U, but there are some that are only 1kw-U
there in such a large locality as LA.

The FM side is no different. I once was on the 405 in Orange County
and started to lose KMZT before the John Wayne airport. KUSC wasn't
much better.

Also, there are translators and other things that attract listeners.
Translators usually cover a much smaller area, some only run on a few
watts, most outside the Northeast and Southern California can have up
to 250 watts or more, and cover large areas, almost as much sometimes
as a Class A FM. LPFMs also have taken to streaming.

Religious stations like K-Love thrive on streaming. In fact, K-Love is
usually in the top-5 of streaming stations as far as total time spent
listening.

Also, non-broadcast outlets like BYURadio at http://www.byuradio.org/
(although they have a satellite feed on DISH Network, and are on one
LPFM), and KZION at http://www.kzion.com/ have streams and pick up
quite a few listeners. I don't think either of these have hit the
top-50 in terms of TTSL yet but well could. There are others that have
made the top-50 that are not broadcast either.