Question: My guess is it just made parsing easier, but I can't see exactly why.

So what does this have ...

```
do
{
  some stuff
}
while(test);

more stuff

```

that's better than ...

```
do
{
  some stuff
}
while(test)

more stuff

```

Answer: 
Because you're ending the statement. A statement ends either with a block (delimited by curly braces), or with a semicolon. "do this while this" is a single statement, and can't end with a block (because it ends with the "while"), so it needs a semicolon just like any other statement.
It's because while statements are valid within a do-while loop.

Consider the different behaviors if the semicolon weren't required:

```
int x = 10;
int y = 10;

do 
  while(x > 0)
    x--;
while(x = y--);

```