"Bless you" is sort of like the Christmas phenomenon, semi-lessening its impact--but still disconcerting when you hear it all the time and stop to think about its roots. In many ways, the U.S. was founded as a Christian nation--not legally, but culturally.

But other religions tend to receive the legal protection and sanction of religions only insofar as they resemble Christianity.

Exactly. Islam is justified as, "well, they worship the same god, just under a different name," and Hinduism does have one higher god in the pantheon (Brahman?). Whereas Native American and pagan religions are blatantly discriminated against, cf. the U.S. military refusing to recognize the pentagram (I think?) as a religious symbol on tombstones.