Its hardly surprising that as the machines get more complicated these things happen.
I'm not sure that the drive is more complicated, but it's a mechanical part and it could have been damaged in transit. They are nowhere near the level of returns that Sinclair had with the spectrum in the 80's.
commodore shipped known bad computers to meet demand, knowing that instead of buying a competitors product that was in stock the customer would have a broken computer under the Christmas tree. They hoped that they'd have manufactured enough working ones before people demanded a refund.
