Mind you, let's not make this a purely Star Wars thing. The number of women in the OT might be absurdly low, which is very notable, but even if there had been more they wouldn't have done much. You could argue that it is based on a genre (early 20th century sci-fi) where attitudes were different- this applies just as much to Indiana Jones.
It's really part of fiction in general. Take the Matrix- again, a strong female character in Trinity. But what is her purpose? Again to be the love interest for the lead- indeed, the whole plot literally depends on Neo being in love with her. And many of her more positive aspects are, frankly, routed through her... being like a man.
Two decades between Star Wars and the Matrix, but it is only the presentation that has changed, not the fundamentals.
But all that said, Star Wars is particularly guilty; scantily clad female syndrome all the way (note Obi-Wan never felt the need to fight topless).
And I would widen this accusation to virtually all Star Wars media. I know the EU is very wide and what-not and has had room for female characters (even a female Sith who isn't a sexy boob-focussed fighter in KOTOR 2, though sadly they made a pants-up of that), but frankly when people think of a Jedi they think of a man and when they think of a Sith they think of a man and the whole mythology is almost stiflingly male dominated.
Of course, the planet we charmingly called "planet of the force moos" is a bit of a crowbar-to-the-face way of making the point, but that's half the fun of Star Wars. You keep things simple and direct and have fun with it.