There's two levels of jargon going on here: PC role and Monster role.
They are different, despite two terms overlapping (leader/controller).
PC role jargon just formalizes the idea of classes with similar job descriptions: a fighter, barbarian or paladin was expected to fight in melee and soak damage (tank, now defender). A wizard, sorcerer, or psion dealed out massive damage to large areas of foes (nuker, now controller). A cleric, druid or bard was supposed to buff and heal (healer, now leader). Rogues, scouts, and monks did damage and had high mobility (skirmisher, now striker). All the role is there for is to tell players the general function of a class and what that class swaps out for (a warlord is as good at healing/buffing as a cleric, so if you have a warlord, you have the cleric's role covered).
Now, Monster's never had such neat little titles before (late 3.5 and) 4e. However, most DMs knew that you didn't run a mind flayer like a fire giant like a choker like a kobold. Each had their own strengths and weaknesses. 4e just put terms to that. Needed? Probably not. Useful? I think it makes creating monster "teams" easier, and I can balance them in roles like my PCs balance their "team" in roles.