Unfortunately it's true, men are driven by physical appearance like Jarett said and this will never change. It's not our fault, it just comes naturally. With that said, I hate it when girls just sulk about not being about to get a guy because they're a bit overweight. Rather than spend your time crying about it be more proactive and do something about it.
Overweight guys have this problem too, although women can be attracted to a man who is slightly overweight, if his t-shirt is hanging off of his belly they won't find him attractive. The thing is that men are naturally 'big' whereas women are not.
The thing is that some women think that they are 'overweight' when they are just naturally curvy. The thing is that you compare yourselves to those women you see in the magazines and those women are what is attractive today. Go back and look at ancient Greek or Egyptian women, here's a link to a picture of one:
link By today's standards she wouldn't be considered model material. Well that's part of the problem and the thing is models are kind of an exception to the natural norm so if you look more like her then there's really no problem. The actual problem is that this natural norm and what is considered the societal norm are different.
That being said, you probably want to look even leaner than the woman in that picture. How do you achieve this? Working out. 1 lb of additional muscle burns an additional 75 - 100 calories a day, and the amount of strength training to achieve and maintain this is only one hour per week.
In addition to this nutrition is also key. A lot of people are fat because they eat fatty foods full of empty calories. The excess calories that the body doesn't use turn to fat while you sleep, making you gain fatty tissue and increasing your physical size.
I wrote an article, it's kind of technical and kind of long being 5 pages in length, but if you're interested in reading the most effective way to get in shape I'll post it for you. The reason for it being so long is that it explains everything in detail to give you an idea of how the body works and show you that most of the things you hear in the average gym are actually fitness misconceptions.
With that said, I honestly don't feel sorry for any woman who is slightly overweight and complains because there is definitely a manageable solution, it just requires a little work. It's also important to note that there are extremes such as 'obesity,' but much like it was in ancient times obesity mainly results from an imbalanced diet of too many carbs. The thing to understand here is that Also, obesity can actually be caused by certain medical disorders, but in most cases unless they are diagnosed as suffering from type II obesity or above it's usually due to poor nutrition.