Democrats know that, strategically, Big Bird is something their AVERAGE base and yet-undecided voter can understand, and it allows them something about which they can act indignantly anti-Romney. This voter likely has NO idea what Romney is talking about, i.e., that PBS is funded by taxpayers, and incidentally, that Sponge Bob or Dora the Explorer are NOT.
If you ever have to engage in conversation with these people, don't try to explain President Johnson, CEO salaries, or PBS bias. Do your best, instead, to illustrate that Big Bird and Jim Lehrer (and friends) are SO iconic and indispensable, they are capable of competing against Sponge Bob and Piers Morgan on their own two feet. Teachable moment.