I install low voltage security equipment and our transformers always plug into the bottom outlet with the ground down. The transformer secures to the screw in the outlet and hangs down keeping it secured.
We used to joke that they were still reeling from the Great Chicago Fire (which, of course, pre-dated electrical wiring).
New York didn’t (doesn’t?) allow T-type 20A receptacles, so you can’t plug a normal straight blade cord into a 20A outlet. Presumably they were relying on the proximity of Canada (same thing) to ensure a sufficient stock of receptacles.
Back to the original question - the NEC states that the AHJ (authority having jurisdiction) has the last say on what is / isn’t allowed. You can be as much of a “code lawyer” as you want, but if you don’t make the local inspector happy, you’ll be doing it over.
Side note - it’s actually rather difficult to get plain-old “crinkle finish” painted metal wallplates these days. Most are either plastic or pseudo-brass. And forget it (unless you special order) for oddballs like “1 switch and 1 blank” or “3 switches and a receptacle” - it seems that manufacturers expect everyone to use cheap-looking snap-together “jigsaw piece” wallplates for those applications.
I just bought a GFCI duplex receptacle from a local big-box store (Menards) that seems to indicate that its ground should be above the parallel prongs. It is a “Smart Electrician” brand, and is tagged “Intertek 4008942” and made in China. If I hold the device in my hand with the ground prong hole above the parallel holes, and then turn the device over while keeping the ground prong hole up, the printing molded on the back is right side-up, and I can read it. This seems to me to indicate that the ground hole is expected to be up.
I wonder if this is normal for GFCI receptacles, or is it an Intertek standard, or did the Chinese factory get things upside down?
Something else that occurred to me: does an installer typically flip the receptacle like an American coin - that is, long end over long end - so that for the “Smart Electrician” case, he can read the print on the back? If that is the case, maybe the installation is expected to be ground prong down.
zombie or no
the test and reset buttons on the front of the GFI receptacles have printing in both directions for the user.
Worked for me, 43 years ago and I still remember that jolt.
I’d still have done it even if the outlet was upside-down 
My vote goes for ground-down, but cocked at a 45 degree angle… just to make sure everyone is slightly miffed.
Most flat to the wall extension cords that I have seen work best with the ground plug down. If the ground plug is up then the cord ends up going up and then has to loop down to the floor. I’ve had to turn outlets around to prevent this from happening.
But I can see where you may want the cord to come out the top and go straight up as well. So meh I say. 
Since a really unfortunate incident with a Stanley tape measure I’ve always installed them ground up, but that’s just me. What are the odds you’re going to drop a thin piece of metal across the two live prongs?
In the UK, I have never seen a socket that is not oriented with the earth (ground) pin at the top. The live holes have a shutter to keep little fingers out which is displaced by the earth pin. Also, the live side is always on the left with the return on the right. I know that it makes no difference with alternating current, but all switches except at the main input are single pole, so it’s important that they all break the same feed.
There was a fad for fitting so called ‘child safety plugs’ a few years ago until it was pointed out that by turning them upside down, a clever child could push the earth pin in and open the shutter on the live socket.
Speaking of UK (and Europe), does anyone know why plug sockets are sometimes in the middle of the wall instead of at the bottom? It’s better from a child-safety standpoint, but I’m not sure if that’s why they do it. It seems unsightly to have a big socket right in the middle of the wall.
that is more convenient for table top use especially when things aren’t left plugged in.
in workshops, where things might be hung above or where you are doing lots of action with metal objects nearby, people might mount them that way.
also on kitchen counters then people might do that.
also people have claimed when they use a decorative metal face plate they would do that.
I was 10 years in Ireland, and every receptacle I saw (in buildings with updated or modern wiring) had the ground (earth) blade slot above the live and neutral slots, and the live was on the right as viewed. Residential (domestic) voltage was 220 to 240 volts.
On a plug I brought back to the U.S., the blades are all solid, and 1/8-inch thick. The ground blade is about 5/16-inch wide and 7/8-inches long and bare. The live and neutral blades are about 1/4-inch wide and 11/16-inch long, and both are insulated for half the length. That way, the metal of the live and neutral blades aren’t exposed until the plug is halfway withdrawn. The ground blade is oriented vertical and the neutral and live blades are oriented horizontal, and are side-by-side. This plug is rated for 250 volts and 5 amps, and molded on it are “BS-1363/A SEC-037”. BS stands for British Standard.
When we built our video room at the town hall, I had all sockets installed in the middle of the wall because that’s where I would be plugging in stuff. No reason to reach down, behind a desk where you can’t see anything. Very convenient.