Since the Rottweiler breed began to seriously evolve in Germany in the 1800's, Rottweiler tails have been docked.
For the most part, the only time you would see a Rottweiler with a tail would be in dogs that have come from a backyard breeder.
One that didn't know what they were doing, or just didn't care or want to dock the puppy's tail.
However, laws are quickly changing all over the world to ban tail docking in all breeds. You can view this chart at Wikipedia that shows tail docking restrictions by country.
Although the chart is still incomplete, you can clearly see that the trend to ban tail docking is spreading around the world.
The ADRK changed the Rottweiler breed standard in Germany in the year 2000 to read as follows:
laws in the United States and AKC (American Kennel Club) breed
standards remain unchanged for now. Although Rottweiler tails do not
conform to the AKC and ARC (American Rottweiler Club) breed standard,
they are allowed and not considered to be a fault at this time.
Only time will tell how this issue will play out in the United States.
I did. . . and after thinking about it, noticed
that most of the dog breeds in the working class and herding class have
their tails docked.
So I did a little research. . . . It actually makes good sense why their tails were docked when you consider their history and origins.
Way back in history Rottweilers really were working dogs that drove cattle and pulled carts and such. This meant driving through brush, brier, mud and you name it.
Dogs with tails would drag them through all that muck and mire, get stuff stuck to them, get cuts on them, etc. which would cause uncleanliness and possible infections.
Even if a poor butcher could or would be able to care for their dogs the way we can today, veterinarians and antibiotics weren't exactly prevalent back then. Rather than lose a valued member of their workforce because of an infected tail, they opted to dock the tails instead.
You'll find pretty much the same story for almost all the other breeds in the working and herding groups with docked tails, as the breed standard.
It's also been rumored that at some point in the evolution of the Rottie we know today, that some were actually born with a natural stumpy tail. However, I couldn't find any documented facts to back it up.