Actually the reason for one
Actually the reason for one outlet part being bigger has nothing in common with dcc wireing. In the ac case it is because in a three prong outlet you have basically one hot wire, and two grounds.
Now the government and the manufacturer wants to make sure that if something happened in your table lamp for example, and a wire rubs against the metal of the lamp it does not shock you. They do this by making sure the lamp has a good ground.
Now if you have two wires then either of them could be hot or either of them could be the ground. This means there is no way to make sure that the lamp will ground out a short, as you can't predict which wire is hot. And only the hot wire matters in a short.
So they make one blade bigger then the other, and thus they know what wire will be hot and what will be ground so they can wire your lamp in such a way as to minimize the chance of a short in the lamp grounding out though you.
This also helps with modern electronics but that gets to complicated to discuss here.
So in fact your lamp really does not care witch way it is wired nor do you until something goes wrong. And really most lamps don't take advantage of this either, I just used a lamp as an example because most of us know how a lamp works. And if you don't you probably should not be wiring anything even dcc.
As far as dcc goes it is not really ac. It is pulsed dc that alternates the direction of flow very very fast. Kind of like what would happen if you you used a dc power pack and flipped the reverse switch thousands of times a second. This is why a dc loco on Dcc track does not move. Because the motor starts to spin one way then the current reverses and it starts to spin the other way, this happens thousands of times in a short order and thus the engine never moves.
As for the needing a reverse unit. Well at any give one thousandth of a second rail one is positive while rail two at that same time is negative. So if rail one ever makes contact with rail two you will get a dead short. Standard wireing issue weather we are talking a c or d c.
Now you could leave a small gap between the two rails like you do with block gaps, bu when a metal wheel crossed the gap it would connect them and you would have a short.
If leave a dead section of rail in between then a wheel won't short the track, but the current flow in The engine would as it was in both sections at once. Now if we make the unpowered section longer then your longest engine the track would not short, but the engine would stop and you would have to push the engine across the unpowered section. Not much fun.
Now if you used a pusher engine at the rear of the train that may work. As the pusher would have power and push the front engine across the unpowered section, and the the front engine would pull the pusher engine across the unpowered section. But that is a bigger pain then it is worth.
Remember in DCC the engine does not care witch way the polarity of the track is. But as per basic electrical theory, you can not allow two sides of a circuit to touch.
Please note that the above examples are massively over simplified. But the basics are correct and anything more accurate would have made an already to long post into a small book.
So to the original poster, I suggest that you get a basic electrical book for beginners, as well as a basic model railroad wiring book, and then after reading those you get a basic dcc book. Because, while dc and dcc as used on a layout, will probably not hurt you if it is messed up, it could cost you a fortune as it does your decoders, or in the worst case, burns down your house.