But these numbers shouldn't be used to determine what size to make a website. I'd guess most people with 1920x1080 monitors don't maximize their browser.
Many web sites are not designed for people who retain older technology for financial (or other) reasons. Every web developer should befriend someone over the age of 60 and watch their surfing habits.
While this site is sort of useful for looking at screen size, it gives the false impression that users don't scroll. They do. Don't ever show this to anyone that isn't fully aware of this, else you'll fall into the trap of trying to put everything "above the fold", a terrible prison to escape.
Above the fold design is critical from a marketing standpoint. But you're right, everything doesn't have to be above the fold.. if anything the above the fold should be designed to encourage readers to scroll below the fold.
One thing to note is that if you have a site that dynamically re-sizes according to the browser window (by for example using percentages in CSS), then you will physically have to drag your browser bigger and smaller to see how much a user with a smaller display size would see.
Really? I always maximise my browser and usually dislike not having windows full-size on my screen. It just gets fiddly otherwise. Also I like leaning back as I surf, and I need a big browser window and 120-150% page scaling for that.
Using someone else's computer with a browser that isn't fully maximised irritates me, but I generally only see that on Macs. I don't think it's very common on Windows.
Everyone is different. I know a ton of people who always browse with 80+ tabs open. I find I fall into that weird trap sometimes too. Though because I have iChat and Twitter open, my browser is usually never full screen.
I would not be so sure at that. I see plenty of people doing that.
It's mostly habit, I think. Even somewhat technically versed people do that (many of them who have been working with computers for more than 15 years).
But these numbers shouldn't be used to determine what size to make a website. I'd guess most people with 1920x1080 monitors don't maximize their browser.