That explanation is both confusing and confused. The "carrying" rule has not been taken out, nor is it redundant. There is no rule forbidding double hits. A double hit is legal provided that both hits are part of the same stroke motion. The relevant rule, which was introduced in order to prevent the S-serve, is that "the server's racket shall initially hit the base of the shuttle". The correct interpretation of this law is as follows: you must not hit the feathers first; you must not hit the feathers and base together. You may, however, hit the feathers AFTER the base. Of course, this would be a double hit, but we now know that those are legal, don't we?