I am sorry to have to tell everyone this, but you are right, women ARE shirking their toilet seat duties. Unfortunately, they way you think they are is not exactly correct. The toilet seat does not simply consist of the seat itself, but the seat AND the lid. In a proper bathroom, when the toilet is not in use both the seat and the lid should be DOWN. Yes, down, closed, completely, so you can't see the water. Women who leave the lid up are just as unmannerly and disrespectful to their housemates as the men that leave the seat all the way up. It's not about women falling into cold water in the night, it's not about men sprinkling on the seat rim; it's about GERMS. When a toilet is flushed, some of the water in the bowl is aerosolized and sent flying in the air. That water includes the germs and other um, particulates, that might have been in the bowl. Studies show that the fine particulates launched by the average flush can spread several feet and can linger in the air for several minutes, allowing the dirty water to settle gently on any surface in the bathroom. Those surfaces include doorknobs, counters, soap, towels, make up...your TOOTHBRUSH! Hopefully, you washed your hands when you were done in the bathroom, but if you left the toilet lid up, you essentially just tinkled on your toothbrush, or worse!
(For the straight dope story, check here: http://www.straightdope.com/classics/a990416.html.)

EVERYONE, men, women and children alike should lower both the seat and the lid after using the potty and before flushing. Men who prefer to stand should lift the seat, and with it the lid, to prevent any splashes or drips and then lower both. Ladies need to lift the lid and then replace it! If the lady in your life has been scolding you for leaving the seat up, please take this opportunity to scold her whenever you see the lid up! What's good for the goose, is good for the gander, or in this case, vice versa!