I think it's simple. They use that definition of indecency to retain a very broad range of power, but will choose to use that broad power selectively. The ridiculously broad definition gives them carte blanche to go after easy targets when they feel they need to (i.e. when enough of their constituents write them letters saying they'll refuse to donate money to their political party unless they do something about it.)

In reality, the FCC doesn't care how bland or "titilating" the material is, they just want to make sure the material doesn't cost voters or political dollars.