I know that's a bit more extreme than the <6" mentioned in the article, but I think it still holds that when making a flagship packed with good cameras, battery life, and CPU, it's much easier to make a sexy looking large phone than a small phone.
And, when it comes to 'pocketability' I find pockets generally trend to expand depth-wise to accommodate thicker items. I've yet to find a garment with pockets that expand length- or width-wise to accommodate larger items