Debate Moderators

The Presidential Primary Debate moderators have been announced:

PBS Jim Lehrer, first Pres debate, Oct 3 Denver...
CNN Candy Crowley, town hall, Oct 16, Hempstead NY...
CBS Bob Schieffer, third Pres debate, Oct. 22, Boca Raton...
ABC Martha Raddatz, VP debate, Oct 11, Danville KY...

This leaves me wondering, though. As irrelevant as broadcast networks have become, why are 3 of the 4 moderators from broadcast networks? And further, why is the 4th from a cable news network which also has ratings in the dumpster?

But even more than this issue, my main question is, why do Republicans continue to agree to moderators that are clearly NOT impartial, apolitical and generally anti-Republican/Conservative? The moderator's politics and agendas are often quite clear prior to the debates and I always thought one of the points of a good Debate was to have an impartial moderator (or at least someone who could ask equally tough questions).

I know it is tough to find people who are good at impartially interviewing politicians, but there are some out there. Why DON'T Republicans INSIST on impartial or at least "equally" divided moderators?