I still can't get it in my head why each state's electoral vote winner isn't considered an independent event. It's not like the voters of one state wait to see how another state voted before voting themselves. Are you suggesting that there is some event that ties the outcomes of separate states together into one dependent outcome?
-PJ
Precisely. The presidential race outcome in each state will be affected by some factors unique to that state, but in most cases it will be more strongly affected by factors which will affect many states.
For example, if the economy continues to do well, this will improve Bush's chances for reelection in almost every state. If it suddenly starts doing poorly, this will likely hurt his chances. if we catch Osama Bin Laden, this will improve Bush's chances. If it were (hypothetically) discovered that Bush personally intervened to prevent Atta et al. from being deported prior to 9/11, that would hurt his chances.
Although there is a certain amount of statistical randomness in election results, and the 'swing' states' results may be due as much to chance as to outside factors, almost any event which would cause Bush or Kerry to lose a 'safe' state would also ensure that he lost all or nearly all of the swing states as well.