Heheh, you might say this topic hits a little bit close to home, since I've always been one for... creative differences of opinion, but....
well, I guess if one has to have a code, there's a few different ways you could do it:
-a code of conduct that is established by the publisher for all clerics of a given alignment/ethos
-a code of conduct created by the publisher that is world or setting specific, usually to a specific deity or faith
-a code of conduct created entirely on the local level by the group playing the campaign.
Obviously, the lower two levels is probably the sort of code of conduct you'll get the most support for. I think making a universal code of conduct for any cleric of a given alignment is askin' for trouble, since it's going to vary a lot by world and god. The paladin is a pretty iconic straight-laced goody-goody archetype (not that you heard that from me!), so that's probably why it's more concrete for them.
Of course, the big thing about codes of conduct is that well, they can be [i]painful[i]. They're codes of conduct for a reason, as in, if you break 'em, you'll CONDUCT electricity thrown down from the sky. I had this FRIEND who got struck by lightning, and lemme tell you, I- he felt it for for WEEKS. Now excuse me while I go crawl into the nearest storm cellar.