What nobody is telling you is that this is a feature of cheap mass-produced instruments (like Fender). Quality instruments have the headstocked angled back to the correct angle so that strings always go across the nut just so.
But now think about this. If you angle a headstock back that means the piece of wood you saw the neck out of has to be thick to handle the angle and then you saw most of the wood away under the thin part of the neck. Of course you could just glue the headstock onto the neck and you do see this done with certain brands. (Les Pauls) But obviously you can have resonance problems as the wood is two different peices and the grain is not the same or same angle in both pieces. Plus the joint could fail over time.
Leo just said "to hell with it, I"m not spending all that money on wood for my instruments!" He just lowered the headstock just a tad and shot it out more or less parallel to the neck. I"m sure he saved at least a couple of bucks doing that!
But now the strings enter the nut at different angles. The ones from the tuners farthest away have the least angle. And I'm sure Leo noticed that this made his basses buzz at the nut like crazy. So he added the "string tree"! The string tree pulls the strings down that go to the farthest tuners and help stop the buzz.
But of course a string tree costs money too! So instead of some nice roller or the like that would let the string move freely when you tune it, Fender came up with the washer on a stalk thing with two (sharp) grooves on the back. Costs a couple of pennies. Saves 1/2 or 2/3 of the wood to make a neck. And nobody cares.
OK? Now you are initiated and one of us. (never speak of this again except to other initiates)
