Earlier quoted context omitted.
One thing that bites me occasionally with the current browsers is when I'm closing a lot of tabs with cmd-w but go too far and accidentally close the last one and loose the window. Windows close with cmd shift w so this behavior makes sense to me. I like your attention to those shortcuts though I think we have similar standards:)
The three browsers I use have command shortcuts that undo the accidental window closures. Though I have to wonder how much resources are taken by the undo feature.
Really? Not just tabs. The danger is you have 5 tabs open, you only want one of them but you accidentally close all of them, now you've lost the window with the tab you wanted.