one thing that is essential in both things is some crunch/crisp. A good sausage roll's bottom side will be flattened and the puff pastry will have crisped up in the juices that have run out of the meat. Likewise, on a pork pie,, a hot water crust will give you a crisp casing but the bottom again will be crunchy and, when cold, you can always tell a good pork pie, as it should have a little dab of grease where the baker pout it to stop it sticking. Unfortunately, in a previous job, I also saw factory ones being made........yet I still eat them.