I find this behaviour infuriating - there's nothing radically different here about size or colours - it's very easy to walk into any number of shops in any town during the last two years to pick up a 6 or 6S and just decide right there & then.
Yes, Apple do offer a return policy, but I personally think it's taking the pish to order a selection with premeditated intent to likely take it back, particularly whilst leaning on the peer support of a forum full of people excited to receive their preorder & disappointed by the lead time & new pricing.
Returns mess up the stock system and add to the retail price of products for the rest of us who are able to make a straightforward decision on an everyday item. Adopting a child, choosing a pension or buying a house needs some thinking about, picking a sodding phone means looking at a website or walking to a shop tops.
spending on what is close to £1000 on a consumer electronics device is not something all can do lightly. Most people want to make an informed choice and fondling the phone for a few minutes in a busy store might not be enough time to make a choice. will it fit in my man bag? can i slide it into my skinny jeans? can I hold it in one hand to text while on the loo? all questions that can't be answered in store.
Apple have not had their arm twisted to over this returns policy, they do so to provide a greater level of customer service and experience. Every customer is entitled to take them up on this.