Whenever I (or anyone else I've seen) have been laid off, and I've been laid off from several jobs, I would have about fifteen minutes to pack my things and say my goodbyes, and be ushered out the door right away.

People that resign may or may not be allowed to stay for the two weeks, depending on how much the company was relying on them (often the companies didn't really have much redundancy or documentation in place and needed to train someone new and/or do a few meetings with infodumps with these people)

But that's the only 'courtesy' I've ever seen.