You know, I never thought of it this way, but it may be...nowadays, in scifi/fantasy flicks, they tend to include an action girl even if the original version of the source material didn't have one.
Best example is Peter Jackon's adaptation of Tolkien's novels. Not that LotR or The Hobbit needed action girls as books, but modern audiences apparently do. It's not a bad thing if done well (they even made one up for The Hobbit).
JJ Abrams did a really good job with having Uhura take a level in badass, so even though I love Urban's McCoy to bits, I approve of the change - if we're not imagining this change of the big three, that is.