I'm probably wrong here, but if the submission for DVD release is exactly the same as the version classified for cinema release, I didn't think the distributor had to pay for reclassification. But if the DVD version differs in any way, the whole film has to be resubmitted as a new release, and the whole classification process has to be paid for again.
But with all the extras on DVD and BD which have to be classified separately, the above probably doesn't apply anymore.