The point about "are" is that C says that small businesses "
are not subject to the same XYZ as big businesses." It would be helpful to provide an "are" to complete the comparison: "small businesses are not subject to the same XYZ as
are big businesses."
In a simple sentence, we don't need this clarification:
I'm not as strong as you.But in a sentence with even a slight bit more complexity, that verb can make a big difference. Compare these:
I'm more interested in economics than you.
I'm more interested in economics than you are.We would probably figure out the intended meaning in the first case (especially if we consider ourselves more interesting than economics), but the second is clearer.
Now look at a sentence with a more involved second half:
The singer is less excited about the concert than the legions of fans seeking her autograph.This sentence is truly ambiguous. Is she more excited about the fans than about the concert (notice my second "about" to make that clear), or are the fans more excited about the concert than she is? Let's rewrite to indicate the former meaning and then the latter:
The singer is less excited about the concert than about the legions of fans seeking her autograph.The singer is less excited about the concert than are the legions of fans seeking her autograph.Here, we put the "are" before that long noun phrase at the end just to make it easier to catch. We could technically put it at the end, but it would be less useful there--by the end, either you've interpreted the meaning correctly or you haven't, and so it's better to make the intended meaning clear sooner.