Although religions may have some fundamental similarities at their core, they are often expressed differently and usually require different behaviour from their practitioners. I have no doubt that religion has an aspect of social bonding with evolutionary importance i.e. it is easier to live in a society where people have the same ethical beliefs, otherwise you always feel others are doing wrong, and other people feel you are doing wrong. i.e. it is a way of genertaing a universal ethic for your society. (This is supported by the use of exclusion of others outside the religion, or missionary action).
Saying this I would say Zen & Taoism are different (call me biased) because they are acutely personal. They also do not have an intrinsic ethical system. (although compassion could be considered part of zen buddhism, it would be expected to arise naturally from a removal of distinctions, rather than being something to necessarily practise).