Online polls are completely and utterly meaningless, as has been pointed out countless times before. The only thing they're good for is confirming your biases, should they agree with the poll.
For reference, talk to President Ron Paul.
Actually, this shows two things. One, PBS viewers aren't all a bunch of far left liberals, as evident by the poll's results. This points to the second thing, PBS must not be as liberal as the far right has been led to believe by their favorite talking head dispenser's of Kool-aid, again based on the poll results.