The short version of EM is the idea that you cheat (or don't cheat) with your heart, not your body. Even "hobbyists" who truly love their wives but also have casual sex with hookers, are practicing EM in a sense, albeit the decpetion neccessary to do so might put in to question the existance of said love.
I'm not sure where you get the idea that people in open relationships think that "emotional monogamy is a silly idea". I've been an on and off lifestyle swinger for most of my adult life, and the vast majority of swingers I've known do pratice EM.
There are a small percentage who practice no form of monogamy at all, who identify as polyamorous, but more often than not, swinging couples have quite a few rules put in place to secure their emotional monogamy. Central to that, is to seperate completely the acts of lust with other people from any form of actual romantic intimacy. Many will not hook up seperately, or go on "dates" with others, or share intimate details about their lives etc...
Though they may deveolp casual freindships with their sex partners outside of the primary relationship, basically they fuck and leave it at that - no further attachments. Now, I can't put everyone in a box because the various rules open couples put in place to secure their feelings of being "number 1" to their SO are widely varied, and sometimes not at all equal between both partners. But the core premise is a pledge to love and share their romantic feelings with only each other, but enjoy the freedom to have casual sex with whom ever they please (unless of course their are rules about that too - some spouses demand the power of veto if their SO wants to hook up with someone they don't personally like). I've heard it all, and some of it makes no sense to me, but to each their own.
EM is not supremely important to me, but I tend to gravitate that way by nature. I don't feel the need or desire for more than one deeply romantic relationship, the way I do for multiple sex partners. And women, generally, in my experience, are predisposed to that way of thinking as well, so that's how it works out. But polyamory would not be out of the question for me given the right circumstances.
To the second question - I think placing a laundry list of rules on your partner - what to do with their body being one of them - is pointless (because when you are not around they will do whatever is in them to do regardless), and shows a lack of confidence and trust. It's suffocating, and can sometimes border on emotional blackmail. As I see it, the primary purpose of such a rule is to help ensure that they retain sole posession of that person (for lack of a better term at the moment). I find posessiveness unattractive. And, it never acheives its intended purpose anyway.
Rather, I'd prefer to be with someone who is with me by desire and not any form of obligation imposed, pressured, or even suggested by me or the rules of polite society, and trusts that I am there for the same reason. I did not intend to single out sexual monogamy, I only mentioned it specifically because it was pertinent to the topic.
The other reson for imposing sexual monogamy, of course, is to follow the rules of our oppressive and delusional society of false morality, which suggest, or rather demand sex only exist where there is love, or those even more obtuse who think they are one in the same. But I digress.
Now, I can predict someone saying that by those standards, isn't EM a form of control as well? Certainly we can not tell others who to love, the heart wants what the heart wants as they say. But, if there is no emotional contract at all, then do you even have a relationship to begin with? I think not, so it becomes a moot point.
I don't see rules 1,2,or 3 as being controlling at all, but as you said, they are just what you expect from good right-thinking people. You are correct in your last statement. Rule 4 is more a philosophy of life than a rule, and the others, really are not rules at all, just deal breakers. What can I say, I'm not big on rules.
Trust and respect are my minimum standards, and no long term relationship can exist between me and any other non-business associated person without them.