It has been discussed here before, but anyway:

• Citizens don't elect the President; states do. All states have delegated the right to choose electors to the voting population, but they did not have to, and they can change their mind. See, for example, here. (BTW, regardless of my usual agreement with AlterNet folks, I think the Supreme Court was right on this one.)
  
• Each state has the right to delegate as many people into Electoral College as they have members of Congress. In other words, smaller states have more that their proportional share (because of those two guys in the Senate). This was kind of compromise between "each state one vote" (good for smaller states) and "each citizen one vote" (better for more populous ones).
  
• From the previous two it is clear that states have the right to choose how will popular vote be reflected in the choice of delegates to the Electoral College. Most of the states have "winner takes all" approach. Several have proportional. (If all stated had proportional representation in Electoral College, there would be no "battleground states".)
  
• In most states parties appoint electors. Somewhere they appear on ballots. In one or two states the voters actually choose electors.
  

Now, why is this unlikely to change:

• Small (populationwise) states like the present situation, because thay have up to three times bigger clout per voter than the most populous ones.
  
• Even the change to proportional representation (as opposed to "winner takes all"), which would mean that, for example, in Florida four years ago one electoral vote would be contested, not 25, is unlikely. This is bacause generally the same party that dominates presidential elections in a given state controls the stat assembly (or whatever it is called), and don't want to give, say, 40% of electoral votes to the competitors.
  

There are more details, some more cynical interpretations etc, but this is the gist of it and I have to go back to work.

Cheers!