I second Seige’s experience.
I’ve lived alone (or with other women) for roughly 90% of my adult life. Before that I lived in my parents house where (as a matter of respect for my mother’s wishes) the seat went down. I am not at my best at 4am when rising to attend urgent bodily functions. This is a task I perform on autopilot, since I’m trying my best not to wake up fully. The goal is to interrupt my sleep as little as humanly possible.
When I’m in public - or in other people’s homes - or just actually awake of course I check before I sit. And I leave everything the way I found it. I have never had a rude surprise under any of those circumstances. But in my own home, 75% asleep shambling to the restroom without turning on the lights and attempting not to trip over the cats, I’m clearly not in full possession of my faculties. There’s enough ambient light in my bathroom to make out general shapes (i.e. I can tell generally where the tub and toilet and sink are), but not enough for a clear look, which I’m not capable of under those circumstances anyway (blurry sleep-vision, no glasses, and a choice between light-dazzlement and darkness). Besides, I’m in my own home, where experience has taught me it is safe to sit. This is even true as I live with my fiance - I am almost always the last person to use the throne at night. The only time I’m not is if he’s also risen in the night to tend an urgent need.
Which means that I only need to be worried about a mistakenly left-up seat if he’s managed to rise in the night without waking me to tend his business and then forgotten to put the seat down. Not a common occurence - I’m a light sleeper usually. My still-sleepy brain knows this - it’s all part of the habit of much repetition. It’s not like lots of thought and tactical planning are involved here. Getting up in the middle of the night to pee is something accomplished almost totally by long ingrained habit (at least for me - YMMV).
So it’s not like ladies get the icy-cold surprise a lot - it just makes a memorable impression. I think it’s happened to me a grand total of 3 or 4 times in my entire life.
The truth though, is that a lot of ladies aren’t necessarily so concerned about the seat issue as the underlying issue of courtesy. It’s a minor request - and most of us do phrase it in the form of a request (at least when we’re living with the gentleman in question - if we’re not, then common courtesy dictates you acceed to the request while in someone else’s home). And there are valid reasons for it - it’s not totally random and senseless. Plus, it relates to an event that happens multiple times daily - as opposed to one relating to something that isn’t a constant occurrence. Yet, when we make this minor request, an enormous number of “gentlemen” either behave as though we’d asked them to donate a kidney, start justifying fervently why Og intended the seat to be UP, or agree to do so and then attempt to weasel out later when we ask them why they’re not doing it.
Which leaves the lady in question (or so my experience has been) with the exciting feeling of a combination “You-think-I’m-a-demanding-bitch” and “I-asked-for-a-minor-favor-and-you’re-being-a-jackass”. Things often go south from there.
And, may I add, a big, hearty :rolleyes: to the folks that seem convinced that asking a minor personal favor of a loved one = demanding. To me (and a lot of other ladies), this seems like a minor favor, in the approximate league of “hey could you not use the soda cans we recycle as ashtrays” or “please rinse out dishwear used to contain milk and/or milk products in the summertime” or possibly “please don’t download things onto my computer” or “please don’t move the pile of paperwork on my desk - I know where everything is”. Not deserving of the drama and controversy 
(As an aside, it’s not a topic of discussion in our house - nobody cares that much about the seat other than use of the lid as a Cat Defense Mechanism as our furballs are mightily enamored of the game of batting various toiletries off the counter with occasional hits into the bowl, including toothbrushes, makeup, perfume, toothpaste, bars of soap, etc.)