Moral: process isolation does not mean better user experience.
No, the moral is that process isolation isn't a magic bullet that somehow prevents all types of browser crashes. But that doesn't mean it's not a useful technique for reducing the impact of things like a buggy plugin.
Like I said, it doesn't magically make all nuances go away all by itself, it may make the programmer's job a lot easier but it does not directly impact user experience.
That's why it's not appropriate to compare browsers based on whether they implement this or not.
Last time I checked if I crashed one instance of Flash player in one tab, all instances crashed in all tabs.
Run Chrome
Open a lot of tabs
Open one with a HTTP auth that brings up the native browser login dialog
Switch to another tab
Close the one with the dialog
Result: whole browser crashes.
Moral: process isolation does not mean better user experience.
Like I said a lot of times:
IE 6 is still officially supported
IE 9 is not available on XP
This is why Microsoft is still crippling the web.