I think leaders would still be there if you were your own ally... it would make leaders a lot more funny to play...
at least spells which should affect the whole group should usually affect the leaders themselves too. (Why are you the only one who doesn´t regain hp when you hit the enemy etc...)
Self-excluded buffs can even be counter-productive.
Let's say you are a leader. You add a new buff to your repertoir, buffing some property X in order to help you party. That can have one of two consequences:
1) The buff does not influence the combat balance. Then the buff is insignificant, and that is pretty depressing.
2) The buff does influence the balance. Nice and good?
Well, since the DM usually sends monsters of a carefully selected difficulty level against the party, battles suddenly starts to be easier than intended. The only way to restore the balance, so that the DM gets the battles he wants, is to increase monster difficulty (typically by raising their level).
So the DM restores the balance. Suddenly the party is back where they were before the buff was applied; things are just as difficult as before.
Except for the leader, who is excluded from the buff. For him, and him alone, the balance has shifted to the worse... And he is forced to keep applying the buff, as removing it will suddenly shift balance to the worse for the party. And the buff is probably something he has paid for, usually from a limited number of feat or power selections.
So the end result of the buff is that everything stays the same, except for the leader, fow whom things are worse... and he paid for that.