Everything just goes somewhere in C:\windows\... what could go wrong.
Well, even Windows puts user files under C:\Users\{username}.
But when you reformat, everything under C: is lost. You could set up things to have the OS in C: and user files in D: so user files can be saved in a reformat, but then you have to worry about the size of each partition and make sure it's appropriate.
That said, when installing apps Windows certainly does put stuff *everywhere*.
All that said, I'm a bit surprised that they care so much about ChromeOS being able to reset without losing data -- I mean, the important stuff is stored by Google as a part of your account anyways. "Safety reset preserves local data and apps, as well as things like bookmarks and saved passwords" -- well, local data tends to mostly be caches, and the rest of what's mentioned is stored in one's Google account.
The big exception I see would be Android apps if they're being used (is this a commonly used feature?), and most of them will have their own cloud storage setups when needed.
Still, the less that needs downloading, the faster the device is back up and working. Bookmarks and passwords would re-download in a second, but apps could take minutes or an hour on a slow connection.