seriously
why?
Because in Saudi culture, that's what men do. It demonstrates their closeness, their friendship, their kinship.
I can only assume bush was trying to be on his best behaviour, to make a good impression on Saudi Royalty. If that's the case, makes you wonder why bush feels the needs to suck up to or kiss up to a member of Saudi Royalty, ...instead of Saudi Royalty kissing up to American ways by... oh I don't know... having a beer & a burger with bush? Shows you the real power structure in that relationship don't it.