I think it's a matter of mathematics. If your channel grows 10% every month, then it will be easier to go from 1000 subs to 2000 subs because you're already working with a larger number. So it does seem like it's easier to grow your channel after those first 1000 (or 100, or 10 thousand) subs.
Even so, as others have said, you can still hit plateaus and there are no real guarantees.