I think if you look at most major Hollywood productions, EVERYONE is there to be looked at - male, female, dog, budgie - even CGI animated rabbits can be made to look sexy (seriously!).
It's a very shallow commercial industry that embraces stereotypes. Ugly doesn't sell - Angelina Jolie will always win in the casting stakes. Kathy Burke is relegated to supporting roles and independent cinema, despite the fact she's an amazing actress.
It's arguable that Hollywood is a major contributor in escalating cases of anorexia with it's impossibly thin body aesthetics - Kiera Knightly being one example.
In previous eras of cinema, women were indeed 'sexualised'. There are countless examples in UK films from the 60s and 70s where the acting ability was zero and the breast size was maximum. See also - Russ Meyer.
With reference to more recent mainstream romantic comedies, I'd say this 'tradition' is in decline. Check out
Shaun of the dead,
High Fidelity or
When Harry met Sally. The female characters are often masculine in behaviour. Interestingly, these are films that appeal to both men and women in equal number.
As for cheesey Hollywood rom-coms - I think the men are just as sexualised as the women. Although it's not a rom-com, Brad Pitt and Angelina Jolie in
Mr & Mrs Smith is a marketing dream come true for some over-paid office flunky - simply because people will pay to look at their perfect bodies.
I think actual gender politics has been replaced by sheer corperatism. If the actor/actress is devastatingly attractive the film will make more money.