Checking the Pieces

I've noticed that in high-level chess games the players almost always move every piece a little bit before the game starts. As if they were checking whether the pieces are glued to the board. Curios! Why do they do that?

Like Kasparov does here on 0:20 - http://www.youtube.com/watch?v=3QXRR9Ql7kI&feature=search

they are perfectionists and they can't focus unless every pieces faces north straight

Just part of a pre-game focus, "getting in the zone" so to speak.  A small, otherwise meaningless pre-game ritual is common enough among professionals who are about to dump all their energy and focus into a single performance or game.

Often, if my opponent has already set up the board, not all of my pieces are centered, and so I do too.  Some opponent's like their knights turned to one side.  I can go either way on this now, but it used to bug me, and I'd face them forward.

It is funny to see it in GM games though, when it seems each piece has been meticulously placed.

Does anyone play with one or both rooks upside down (or only when they've lost the queen from that chess set but they have a spare rook)?