My dealer told me that ADC was not originally to be on GTI's but was later changed and it looks like this was after the first demonstrators build schedule.
We only started seeing GTI demos filtering through 3 or 4 weeks ago. They would have been scheduled for build 6 weeks before that (assuming 2 weeks delivery, which we have seen is very very plausible).
ADC was a known standard equipment for the UK market earlier than 10 weeks ago but as they were MY13 builds they decided not to include ADC (even though it was available to MY13 cars as an optional extra - mad IMO).