We've been married for over five years now, have two little kids and our relationship is as good as can be. We both value harmony very highly and thus tend to avoid an open conflict whenever possible - and so far there was little to none reason for serious conflict, whatsoever.
The "problem" is quite simple: My wife hardly uses the word "please" whenever she asks me (or our kids) to do something. It's not that she's particularly impolite, constantly bossing me around or something - she's always very friendly, it's just that she almost never says "please". I can only speculate but I think part of the reason is "efficiency" when speaking. As a teacher she talks a lot at work and at home, so I think she instinctively tries to avoid "unnecessary" words.
As long as we didn't have kids that didn't bother me at all, but now I think we both should act as a good example for our kids not just teaching them "manners", but actually behaving in the very way we expect them to behave - whenever that is appropriate. (Especially when talking to kids, there are of course plenty of occasions in which you do not say "please" or even refrain from being "polite" for a good reason.)
It is, however, my point of view, that when talking to your spouse the use of the word "please" should be the rule rather than the exception. Of course I do not expect my wife - or anyone - to fall on their knees saying something like "If it doesn't bother you lordship, would you be so kind and pass the salt, please." but a simple "Pass the salt, please." would be perfectly fine.
The "usual" way of asking for the salt would be a simple, friendly "Would you pass the salt?". As I've said: She's not simply issuing commands. There have been outsiders interpreting it that way, but this is rare and it's not relevant for me as I don't perceive it this way and this is all that counts.
So far I've tried to be a good example - maybe even to the point of being slightly "over-polite", though I don't think that is a problem.
I've raised the issue a couple of times primarily focusing on trying to be a good example for our kids plus - less important, but still an issue for me - my personal feelings and my wife said she understands what I'm saying and that I'm "somewhat right", but doesn't change her behaviour - at least not enough for me to notice.
All this is far from being important enough to me as to raise a "major conflict" over it - maybe not even a minor one. I'd prefer her to understand what I'm trying to say (and act accordingly) rather than to just adapt her behaviour "because I said so".