I don't think it's that clear. For instance different incognito windows, opened separately, share everything among them. This was not at all clear to me, though I suppose at least for tabs in the same window it makes sense.
But Safari has its own problems. For instance, despite promising to be a safari I noticed that I am still located in exactly the place I started. If it doesn't rename to Apple Web User Agent then it is clearly misleading to the non-technical user.
That’s news to me, too. Makes sense though. I assume it’s because you can drag tabs from one window to another. So if you open two incognito windows and drag one windows’ tabs into the other, the browser needs to decide what can be shared. You could keep their states separate, but what if you then you open a new tab in that shared window? What state/profile object is the new tab associated with? Just sharing between all windows is easier to handle.
