One of my favorite television quotes is from "Burning Down the House", the first episode of the third season of due South.
"People are not interchangeable like snow mobile parts," says our hero, when his father tells him that one 'Yank' is as good as another.
But, so often in television and movies, women have been interchangeable -- the Bond movies providing a prime example of such a thing. In each movie, there's a 'Bond girl' and Bond's affection for her lasts only through that particular movie, to be switched out for the new girl at the start of the next movie. The Austin Powers movies parody this concept (while, of course, using it themselves).
Many 'action' television series take this same stance -- women flit in and out of the lead (male) characters' lives, only important for as long as they're onscreen, soon to be forgotten (unless the actress returns for a one-shot 'reunion'). Girl of the day, woman of the week, maybe even important enough to make the lead shed a manly tear or two, but rarely important enough to ever be mentioned again.
Action movies (and action/'buddy' shows) tend to assume that their audience is young men, the assumption, perhaps, being that men would prefer to see the hero with a succession of (beautiful, of course) women, as opposed to struggling through a more complex and permanent relationship.
Now, this isn't a problem that's confined to the action genre (nor do all action films contain such issues) -- it's a problem perpetuated by our society, with some people buying into the belief much more strongly than others, people who carry that belief through their work (an example of this would be Kevin Sorbo, who played Hercules in the eponymous television show and, when given more power in the series Andromeda, turned it into a much more action/'hot chick of the week' type of show).
[Side note] That said, it's a prime example of one of the major issues of the writing of movies and television shows -- the writing of female characters as 'women' and not as people (as was said by, I believe, Rebecca West -- "feminism is the radical notion that women are people"). Heroes has several female characters, but nearly all of them are characters that could only be played by women (as opposed to many of the male characters, who could have been cast female without changing much more than pronouns) -- Niki the stripper mom being the most egregious example. [/end note]
Many of the shows that I've watched have had issues of this sort -- many shows that feature a pair of male leads will have a new female love interest every other week or so, to serve the dual interests of propping up male viewership while defusing the homoerotic tension that frequently crops up in buddy shows (of course, the very transitory nature of the love interests tends only to highlight the more lasting bond between the male characters, thus making the show even gayer).
Luckily, I've also watched many shows where the female characters were as essential and as human as the male ones.
And, recently, there have been two places where not only were the women strong and real, the notion of female interchangeability was directly refuted.
The Bourne series not only doesn't feature a series of love interests, it goes to pains to set up a sequence similar to the one that had Bourne kissing Marie in the first movie and then have him not do the same in the third. Marie is not replaceable, even if Nikki kicks complete ass. And that's a good thing (and not a reflection on Nikki's status as a person -- her identity does not (and should not) need to be validated by having Bourne desire her).
On the television side, the show Doctor Who spent a year building up a romance between the Doctor and Rose, a year exploring it, and, just recently, a season where one of the undertones was her irreplaceableness. Martha Jones, the companion after Rose, kicks a lot of ass over the course of series 3. She's also thrown into situations that are very similar to the ones shared between the Doctor and Rose. However, like in the Bourne movies, Martha cannot replace Rose, because women are not interchangeable. The Doctor didn't fall in love with Rose because she was Generic Kick-Ass Female Companion -- he fell in love with her because she was Rose, with all her virtues and foibles.
And so, Jason Bourne and the Doctor become characters that I can respect more deeply, because they respect and are aware that women are people, not living dolls that can be exchanged if they get damaged or lost.