[Stephen]

The reality is that as demo or promo copies are only issued to promote the movie they have only been viewed a handful of times, where as a retail copy will be a copy of a copy made in big batches and viewed hundreds of time so the quality will have degraded a lot.

That's really the only reason. Promo copies will be run off in small quantities and direct from the master.

I have a couple of first pressing records, with plain labels and white slip covers and yes they do sound better but only as they didn't get used much and as the name suggests we're the first copies pressed.