The difference is that ads on websites are somewhat expected and usually easy to block and contained inside a browser.
Ads inside an OS are in a different category of annoying. Especially on Windows where it's not just one setting to turn them off, but they're scattered through the OS, they get re-installed with updates and it's a constant game of whack-a-mole to get rid of them.
I don't get the point of comparing Windows 10 to websites. How about you compare it to Windows 7? Somehow, Windows 7 managed to work just fine without nagging you with ads all the time.
Ads don't have a place practically anywhere. They are annoying in the OS, and also annoying on the websites, in between movie scenes, on the side of city buildings etc either. Reminds me of the Futurama scene:
Fry : So, you're telling me they broadcast commercials into people's dreams?... But how is that possible?
Professor Farnsworth : It's very simple. The ad gets into your brain just like this liquid gets into this egg. Although in reality it's not liquid, but gamma radiation.
Fry : That's awful. It's like brainwashing.
Leela : Didn't you have ads in the 20th century?
Fry : Well, sure, but not in our dreams. Only on TV and radio, and in magazines, and movies, and at ball games, and on buses, and milk cartons, and T-shirts, and bananas, and written on the sky... But not in dreams.
Not really different, it's leveraging users from a product to another. Gmail and Windows users are both stuck and forcefully promoted "unrelated" products (specific ads tied to OS/website so not easily blockable).
I think the point is that if Google didn't do that and been successful at that, Microsoft would probably not feel the need to promote this as much as they do.
My Windows 10 Settings app has a "Rewards" icon. After opening 100 tabs with the Firefox container you get an achievement. On Xbox they have a rewards system for just using your console, like start a few different games.
In the future, the OS will have personalized ads everywhere, "hey buy your favorite cookie now!" inside Outlook, combined with achievements for using it correctly, "Two more emails for Master of Email!"
And of course social interaction, "Ann just saved the file annual report. Do you want to like and share?"
You also have to buy usage time with gold coins or wait 24 hours.
I don't get the point of comparing Windows 10 to websites. How about you compare it to Windows 7? Somehow, Windows 7 managed to work just fine without nagging you with ads all the time.