David Henderson points out a pretty disturbing op-ed from Stanley Fish on why we should differentiate Maher from Limbaugh that basically amounts to "Maher is a good guy, Limbaugh is a bad guy, so the double standard serves the cause of the good".
The op-ed was especially offensive to read because there was no need to invoke anything like that to differentiate Maher from Limbaugh. The way I've viewed it is that there are some offensive things we can say that are generic insults, and then there are specific commentaries on behaviors. Limbaugh was identifying women who (1.) use contraception and (2.) are sexually active and (3.) are open about it and (4.) think it's a worthwhile policy discussion to have as being "sluts" or "prostitutes" because they do those things. That's considered beyond the pale because he's passing judgement on these things that most of us think reasonable modern women should feel perfectly comfortable doing.
Bill Maher isn't really commenting on behavior. He just doesn't like Sarah Palin and is grabbing for a mean word to throw at her. It's not exactly nice, but it's a different goal altogether than Limbaugh's.
I wish there was a good conservative counterpart to Maher, but there really isn't that I can think of. Maybe it's best to use an apolitical counterpart like Louis CK. He has a foul mouth and he uses all those insults. But like Maher (and unlike Limbaugh) Louis CK is not vilifying reasonable behavior: he's just lobbing insults.
There's a good reason to be angry at Limbaugh and not Maher, but Fish did not reach for the good reason.