There always seems to be a certain struggle about what kinds of behavior may be labeled, "BDSM". I think that for many, the label carries a cachet that they want, an exclusivity, that compels them to draw boundaries and define what is in and what is out. Compare a BDSM lifestyle to motorcycle ownership. You will find a group of motorcycle owners who insist that if you are not riding a Harley-Davidson, you are a poser. If you said something about motorcycles to some who are not riders, the vision that springs into their minds is of a horde of Hell's Angels riding by with loud motorcycles with no fenders and "ape-hanger" handlebars, intimidating every car they pass. Then there are all of the baby-boomers who wanted motorcycles when they were young, and now can finally afford them. They ride on weekends, and like to wear leather and bandannas. Or they have fully decked out Honda Gold Wings, with heated seats, handlebar grips, satellite radio, nav system, a reverse gear, and now, even an airbag! There is the 20-something on the Japanese bike blasting down the freeway at some incredible speed, wearing a t-shirt, shorts, and flip-flops. Which of these is not a motorcyclist?
So, where, northern_son, is your line drawn? If my GF and I sometimes enjoy blindfolding and tying each other to the bedposts, are we into BDSM, or must I make her wear a collar and chain and eat out of a dog bowl?
Relationships are relationships. There is nothing about a "BDSM" relationship that intrinsically makes it any "deeper" than any other relationship. Anyone who is seriously in a relationship has an obligation of some kind to his partner. What is so special about a D/s commitment? How does it compare to the commitment of someone caring for a partner with Alzheimer's, or MS, or cancer? How much does that person endeavor to "learn" how best to care for his/her afflicted partner? How dependent is that partner on the care of the other?
As for who is a Master or sub and who is not one, there are many who would love to have some kind of certifying body that offers an exam, both written and physical. A candidate would have to pass a written test, then demonstrate his skills with whips and ropes. Each candidate would have had to complete some kind of training and initiation, like a Geisha, or a Karate Black Belt.
People form relationships. They select behaviors that they find mutually satisfying, and have at it. Sometimes a relationship works, sometimes it doesn't. Hanging the BDSM label on it does not affect the outcome.
So what is the point in using the term, "BDSM"? It serves a very useful purpose to help people understand that a certain set of behaviors is being discussed. If a couple meet and one says to the other, "I am into BDSM." it is the same as if he/she said, "I am into camping.", or, "I am into motorcycling." It provides a basis for discussion and a loose frame of reference. If a woman says to me that she is interested in BDSM, she will be much more appealing to me than she would be if she said she was interested in camping or ballroom dancing or kayaking.
And how the relationship works out will be similar to how any relationship works out. "Look, I think you are really a pretty great man/woman, but I intend to be on my motorcycle every opportunity, and I just do not think you are as into it as I want my partner to be." or, "Hey, it is supposed to be nice Sunday, and the motorcycle is gathering dust in the garage. Want to go for a cruise?"
There does not seem to be any point to me in trying to put some one-size-fits-all boundary around BDSM. Find someone who likes what you like, about the same amount that you like it. Make some adjustments if that person seems to be worth adjusting for. If not, go find somebody else, and don't get lost in some arbitrary boundary.