It's not necessarily just the hyphenated last names that are an issue. I can only think of two couples with hyphenated last names that are pretty awesome in my book, but most often than not, those with hyphenated last names are more difficult that your average demographic. I can only hypothesize the reason, but there's two types of hyphenated last names - ones that are inherited and ones that are through marriage. I believe it stems from a different relationship dynamic between two individuals (in either marriage or raising the child that inherits that last name) that deviates away from the tradition of taking the father's last name in your traditional family model. Now, deviation from that, either by "choice" or subjugation of one partner over the other would dictate that some deviation from the normal naming taxonomy that our society shows some kind of struggle somewhere over naming conventions. Anyway, I digress - I find those that refuse to give up their last name in marriage and hyphenate it tend to be dominant over all family matters to the point of subjugating their partner. Now, that tends to translate to people trying to "have it their way" when it comes to their dental work. I don't know too much about the children that receive two last names, but I figure there's something in the family dynamic that could be different in a two parental unit family. This is my line/reasoning behind the observations that I have made throughout the years with people who have hyphenated names via marriage. I'm sure there's tons of single parent families and so on, but I'm not going into that because they usually end up having one last name, and the main issue with a single divorced parent family with shared custody is making sure BOTH parents give consent for their child.
Now, you might say, this isn't everyone. I agree, it's not, and there's one good test to see if the hyphenated last name individuals are problematic before you even see them. If their last name was Mrs. Smith-Jones, have your staff call them Mrs. Smith. If they put up a ruckus over it, then you already know it's a PITA patient.
I'm not a sociology major, if anyone has an answer for this, please post. I'd like to know WHY they tend to be more difficult.