Did Johnny Rotten go to the police and swear an affidavit? 'Cause just saying "I knew it all along" after the fact isn't going to hold up in court.
I mean I'm sympathetic to the idea there was some cover up, but I don't choose it as my default explanation. It's very hard to prosecute rape cases to begin with, and given Savile's image with the public and the esteem people held him in, it seems simpler to just assume the cops/prosecutor were just giving him too much benefit of the doubt.