There are certainly going to be lots of counter-examples, but the fact that two guys and a girl pre-dominate, I think can be explained by the tagline from The Mod Squad: “One black, one white, one blonde.”
Men are the default sex (not biologically, but sociologically, and in literature), and “woman” is one variation on “man.” So there are actually lots of examples where you have even bigger groups of men, and just one woman. In fact, in any group of TV, movie, or book characters, you will nearly always have more men than women. There will be a great variety of men, but the “variety” among the women will usually be one of a few different sets of opposites: blonde & brunette (with fairly interchangeable personalities); whore and virgin; “one of the boys” & ball-busting bitch; extra-smart & really dumb; androgynous & sex kitten. The last two are combined a lot (cf: Velma & Daphne on Scooby-doo). You sometimes get “perfect & loser,” but that’s a lot less common (cf: Ripley and the character whose name I can’t remember played by Veronica Cartwright in Alien; Ripley and the women in Aliens were an example of “one of the boys” & ball-busting bitch).
Rarely do you see women with sui generis personalities, unless they have lots of superficial, cutesy quirks, which is actually a type all it’s own, and not really sui generis at all, when you get right down to it; it’s sometimes a man, but more often a woman: cf: Garcia on Criminal Minds.
One of the things that interests me most, though, is that when you get one woman in a fairly large group of men, she is often the most normal one. Cf: Elaine on Seinfeld– not without faults, but the most normal of all the weirdos on the show. Also, MTM was often the most together person on her show when she was interacting with the men, and in her personal life was part of a “perfect/loser” dynamic with Rhoda.
The Big Bang Theory has an interesting dynamic. Penny started out at just “the woman,” then when Amy was introduced, we had “Smart and Dumb.” Later they morphed into Smart & Dumb as well as Whore & Virgin. Meanwhile, Bernadette comes onto the show as “the normal one,” something you usually don’t get except when she’s the only woman.