One square, or two squares forward?

I was struck by a particular move whilst watching one of yesterday's games.

If I were playing white, and had the above position, I would never even consider h4.

It reminded me of a similarly puzzling move earlier this year:

Again, at the time I was amazed at Radjabov's move, but after reflecting upon it, decided it was a type of prophylaxis, stemming an advance of black's king side pawns.

I am still puzzled by Kamsky's move.

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