This is really quite an interesting topic. I've just read most of the postings, and one thing I particularly agree with is the suggestion that, in certain popular songs, the 'expletive part(s)' are absolutely essential to the feel/message being expressed. For good or bad, of course...
It is a difficult call, if you are a parent. Likelihood is, your children will be exposed to pretty much every word at some stage, and I think too much cushioning can be a bad thing. As to releasing different singles formats for different ages, record labels have for years managed to release CD1 and CD2 versions of singles, in a desperate attempt to increase sales, - normally through change in cover colour/additional 'KOOL' bonus hidden mixed/mashed-up track etc. - thus I suspect it should not prove too difficult to accomodate for the various age ranges in the market, and their respective legal rights.