@DavidS completely agree. Also think when and how you get lucky makes the big difference. For example, Hamilton’s luck in Brazil 2008 had a huge impact – He won his 1st championship by a point. In 2009, Jenson Button lucked in by having a superior car to everyone else and ended up winning a championship because of it.
Similarly, Alonso has had one of the unluckiest moments of 2010, when the safety car period in Abu Dhabi messed up a certain championship for him. Although Alonso has been lucky a few races this year, none of them will matter if his engine blows in Sao Paulo and if he loses the championship because of it.