I've wanted to write this for some time, but hadn't because there was no solid data to back-up my assertions. I do now. This is about why I believe the future of tablets (and by extension, computing) is 15-inches in display size.
Let's start with the origins of the modern tablet. The original iPad played such a strong role in shaping our perception of what a tablet should be, including a 9.7-inch display that we think of standard today. Apple arrived at that size because 9.7-inches was ideal given technology's constraints at the time like weight, battery life and cost. It was the right size for 2010.