Captain Sparklez is hired to shoot a villager, but it goes somewhat awry...
While funny, the video does make an interesting point: how would one normally tell any given villager apart? While 13 distinct professions exist for villagers, there are only 6 variations of outfit for any given profession, as each profession is one of three possible from a "core" profession. Example: the black apron outfit is assigned to smiths, which include the armorer, weaponsmith, and toolsmith.
Perhaps a more curious question: what if all the villagers are clones? They share an identical voice, body shape, and virtually everything else beyond clothing. An argument can be made that everything in Minecraft is like this (every creeper looks the same), but villagers hold a somewhat special place in the game, being the only other apparently sentient species the player can encounter.
Just look at that little guy.
Then again, without adding a skin, every player is technically Steve or Alex. Are they potentially clones too? Beyond sheep, rabbits, and horses, very few things look different from one-another...
In honesty, it more likely comes down to simplicity for the game engine, since it doesn't have to store and render hundreds of variations for every living thing. Nonetheless, it's an amusing theory.
Have a great weekend, Minecrafters!