The way I see i is like this. D&D has it's own fantasy milieu made up of archetypes loosely based on those from medieval European history and legend. The paladin is the holy warrior/knight archetype. There are no archetypes along the lines of the paladin for other alignments to be found in medieval European folklore. The evil equivalents, for example, are fallen knights, which are modeled quite well with the blackguard.
So, you might say, what? Well, look at it like this - D&D is, essentially, its own sub-genre of fantasy. The archetypes it has developed for itself over the decades help make it what it is. d20, on the other hand, is the truly "generic" version of the game. d20 is where altering the core classes, either by exclusion or inclusion, should really occur. What I'm getting at is this - getting rid of the paladin in D&D (as opposed to d20) would be akin to getting rid of the jedi in Star Wars. Some will contend that D&D is "generic" fantasy, but it really isn't. It's essentially its own fantasy setting. That's why d20 is a better place to try to effect such changes.