I didn't want to have to explain this because it is a lot of work, but here goes:
DC doesn't have a ground. It goes from positive to negative. And NO, regardless of voltage (even a million billion volts) will not shock you UNLESS you touch both positive and negative.
AC flows to earth. You'll notice that those distribution towers you see along the highways have 3 wires (for the 3 phases) and the no ground wires (they might have on top for lightning but they are much thinner and not used for anything other than lightning protection). So in an AC system your neutral is ground. The difference is ground is used to detect a problem and to get rid of noise in the electrical system that you don't want on your neutral. Our trip switches in our houses in SA has 2 types of trips, the first is a ground breaker which breaks the connection as soon as a high current is detected on your ground (remember ground = neutral, but it is there for safety and to filter out electrical noise, not to act as your neutral). The other kind of trip is a residual current device (RCD) which detects if your return path is the neutral (anything else is assumed to be ground and therefore dangerous). If your ground breaker trips, that means a high current passed through the ground wire and it cut it off for safety. If the actual trip switch trips that means current was being directed in a path other than your neutral wire (eg. a person).
That is AC in a nutshell and what the difference is there between ground & neutral. As I said before, a ground wire in an AC system is also usually used to get rid of noise (stray AC currents which means it's frequency is different or it is out of phase because of inductance). Noise on a neutral wire is not desirable because it will flow into anything plugged into that distribution before it is grounded.
A ground on a DC system is used because your DC system uses AC. For example an amplifier. An amplifier takes an AC signal then boosts it using DC. This will introduce noise, which is shunted to ground.
A ground loop is exactly as the name suggests. You have multiple ground points in a single system. So it creates a loop in which the noise moves. Ground loops you can easily identify in a car where it'll have a noise as soon as your engine is running. The reason you hear the noise only when the engine is running is because the electrical system is DC! Therefore it has no ground. But an alternator is AC with rectifier diodes and a floating voltage regulator, however it is imperfect so you have noise. If you have a ground loop the alternator noise can be heard on the sound system. That noise disappears as soon as the alternator stops turning.
A PC ideally needs 100% DC, eg. no noise, no stray AC (at any kind of frequency). So the SMPS filters it out. Therefore a ground wire is only needed if you have a very very low quality AC -> DC power supply.
The guys who design these things actually DO know what they are doing. They don't include a ground wire because they rightly know it does not make sense.
Your SMPS or power brick (which is a SMPS) DOES have a ground wire which it may or may not use to filter out the AC noise. But once it is DC you don't need a ground wire anymore.
Do you see ground wires after your PSU in a PC? No, because you don't need it, the noise has already been filtered out, you are working purely with DC and all the noise has long been filtered out (by capacitors).
My 2c
