I know people say that but I think it's a bit of a cliche and only applies to second-rate actors (usually - I think it's tragic that Renee Zellweger has gone down that route, as she's a great actor and could so easily have gone the character actor/older actor route instead).
Much like musicians. "Oh no woman can make it in the music industry unless she takes her kit off and pouts" well, no. Not if you're Adele, or KT Tunstall, or Patti Smith, or First Aid Kit, or Laura Marling, or a hundred other great artists who just say no to that and succeed by simply being good at what they do.
It's a valid point that we should recognise the pressures on women, that some of them succumb to. But I don't think we do enough to really celebrate the women who clearly don't succumb, and are still brilliant and massively popular, because they are the ones who turn the tide. We won't turn the tide by just moaning "oh there are no parts for older women so they have to have cosmetic surgery" and ignoring the women who buck the trend.