I don't watch much TV at the moment and 90% of the shows I have watched in the last year or so have been action/suspense shows like 24 or Alias. I don't know if diversity is the same issue there. I mean, the black President Palmer character in 24 had too big a role to possibly be called token; SPOILER especially when it was revealed that the attempts on his life WEREN'T racially motivated./SPOILER
The reason it's more difficult in sitcoms is because modern sitcoms are hugely based on observational humor and race (whether we want it to or not) will be a factor in observational humor because humans are still flawed barbarians. Couple this with the fact that network execs will lean towards safe and obvious - therefore, "she's canned because she's not Asian enough".
As for news hosts, I suppose CNN International/Asia Pacific could be worse. I mean you get a Syrian/American/French hottie, a preppie looking Australian Aboriginal and a strange British dude with a chainsaw voice. Who could ask for more?