May I ask why? The words have the -exact- same intent, and are thereby expletive by association. May as well just change the spelling to something slightly different, like some appear to do on the internet... it amounts to the same thing.
I'm not trying to offend or say your view is wrong, I just don't understand it... the 'lack of vocabulary' argument makes more sense to me than this one.
Also "God", "damn" and "hell" are technically not expletives, but are considered irreverent or blasphemous, instead.... they are words with normal usage.
Edit:
Furthermore. I theorize that some phrases were in 'proper' use at some point, for example I can imagine how the phrase "get off your ass" may have at one point been a literal saying, which gained the connotation of "stop being lazy". I believe this is possible due to 'ass' being another word for 'donkey', which have been used for traveling, and if the person is not on their 'own feet' when it is believed they should be (e.g. they are supposed to be doing work instead), then it might have been requested that person dismount from their donkey, or 'get off the ass'.