There is no standard for receptacle orientation. Want to get in a good argument that lasts for weeks? Go to an electrician's forum and declare the best way to orient receptacles. Then, as it starts to die down, declare the best way to orient horizontal receptacles for a boost.
Seriously, the argument has been around forever. Some electricians claim protection against flood, although high-amperage sockets are usually several feet off the floor (and well above the standard outlet height). Truth is that if you have a flood that inundates half a 14-50 receptacle, you have a more serious problem on your hands. Some electricians orient all receptacles ground pin up, so that if a metal faceplate comes loose and falls between a plug and the receptacle face, it will only hang on the ground instead of short out the two hot conductors. (On a 14-50 it wouldn't really matter, because you'd have it hanging on the neutral the opposite direction. I was speaking generally about 5-15's.)
Truth is that it really doesn't matter. Install 'em how you'd like. In my shop, they're ground-up; in my house, they're ground-down... preferences based on the guy I paid to install them and I'm not so anal to turn them around. FWIW, I prefer ground-down except 30A+, and they're always ground-up (except twist-lock which is another matter entirely).
(And yes, Tesla's instructions do say ground-up for the strain relief.)
