People are so overprotective these days. Putting an "18+ Only" label on Sesame Street (of all shows) will not accomplish anything.
Slightly OT, but I'd totally watch Yo Gabba Gabba. Perhaps I'm just way out there as it is, but I love that beat. Now, the video itself was freaky as shit.
If anything, it devalues Parental Warnings and guides further - "What?!" a parent would say, "Sesame Street is 18+? I know that's bullshit. Maybe that game Jimmy wanted, Manhunt 2 which was also 18+, isn't so bad afterall...."
This example is a little extreme, but it illustrates my point - the validity of these warning advisories has come into question (or come further into question, depending on your point of view).