Being a sociologist (technically, due to my degree), the engagement ring is to signify love, not monetary gain. Society moulds what love, marriage and committment is to one another, and the engagement ring for women and men signify this.
I think the thing I would look at is if women want the "big" diamond, instead of the small one, are they really in this for love? It shouldn't matter what ring you get, it is the token and thought that counts. This may seem crazy but even if I ever got a 25 cent ring from a vending machine, or a hard rock candy ring from a suitor, it would be the most sweetest thing in the whole wide world, and who wouldn't marry someone after that?
I am a helpless romantic and to me it doesn't matter what the ring looks like or how much it costs, it is the fact that someone is professing their love to you.