HaLeiVi –
Sorry about the Hebrew.
If you look in the Rambam you mentioned he writes that there a list of things which are to make a break from customs of the idol worshipers, one of them being lo silbash, but then he digresses and says that there is anyway the reason of pritzus. And the Gemara I quoted it clear that l’halacha this is the reason.
About u’vchukoseihem, my question is that if we learn from it halachos that relate to avodah zarah then what is it’s relation to arayos. Whether or not it appears more than once doesn’t address the question.