I am totally happy to take on this argument, because it is a totally "PC" related issue that is actually a bit more important than it would seem.
So the problem we are dealing with here is on the unfortunate (and obnoxiously persistent) socially constructed "subtle sexism" that just doesn't seem like a big deal, but its what keeps the problem going.
The big question is why do we need to have separate titles for men and women who are doing the same job? There is no reason why a woman bringing you food & drinks needs to be differented from a man doing exactly the same thing.
Unfortuntaely, in the standard understanding of the difference between "waitress" and "waiter" there is a huge gap. When you first think of a "waitress" (stereotyping here, of course) the image that comes into most peoples' minds is that of a tacky short polyester dress with a ruffled apron and a dorky headpiece. When you think of a waiter, do you visualize sort of a classy dude in nice slacks and a shirt and tie, if not a full tailsuit? (just do a search in Google images...you'll see what I mean. The same goes for the steward v. stewardess argument). Why do we think of waitresses as greasy spoon gals, while the fellows that wait tables are high class gents? The women are also typically portrayed in the images I found as highly sexualized things. The "stewardesses/waitresses" I find look like they are willing to serve passengers much more than a cup of tea...this is why it needs to change. Not because this is true, but we're trying to get rid of stereotypes and automatic associations. So we needed new terms. The industries chose "server" and "flight attendant". That's their choice, we just have to live with it.
The theatre industry is working on a similar problem. The "actress" image is that of a swooning woman in a puffy dress. They decided that all performers are now "actors". There is a lot of enthusiasm for this movement, but the word actor is still associated with the male sex, so the women who choose to be called "actor" immediately get a masculine tag attached. (They're trying).
This is why people in the service industry are using new terms that are (at this point) not gender classifying. Because a person's sex and their ability to do a particular job are completely unrelated and that idea needs to become part of everyday life.
Jobs that have always been traditionally male have never had this problem, so as women FINALLY make their way up the ladder of career success there is no preexisting name to denote gender. I mean, no one has ever heard of an investment bankerette? Or a divorce lawyeress?
Its just another tiny branch of the "abilities and sex are not related" argument, which will continue to arise until women are fully immersed at an equal level in the career world.