Strange. I said, "You've never had a cleric or druid to heal the party?" and your answer is, "I've never had a cleric or a druid lead the party." I don't get it.
"Leaders" in 4e are healers, removers of afflictions, and providers of buffs. If you've had a cleric in your party as your healer, you've had a "leader," in 4e role terms. If you've had a fighter with a big sword who puts the hurt on things, you've had a "striker." If you've had a mage burning things into the ground, you've also had a "striker," or maybe a "controller" if he/she was heavy on the AOE spells.
About the only way to have played D&D without ever seeing the "roles" in action is to have not actually played D&D as it's written. Because the roles are drawn directly from the game.