Theres loads of theories about it, some going off how the greeks used to horse race. Then there the way your water swirls down the plug hole theory(strange considering souther hempisherians(?) dont run clockwise but the one that makes most sense to me is that we read left to right and graphicly represent time left to right so its seems the norm to want to see the finish straight left to right.
Yes, but say your at silverstone and sitting in the stands opposite the pits you'd be watching the finish of the race from right to left, so it's not always the case.