There are many times I wished I could have two windows side by side on the iPad. They both don't need to be running, but I do need to see what is on the screen of both. Having to switch back and forth between two apps is a PITA.
You don't need to hold the tablet or Mac Pro up to your shoulder just use a dorky blue tooth headset. It's not for everyone but would certainly work for a lot of people. For that matter, I wear hearing aids and I can get ones that are blue tooth so I wouldn't even have to wear the dorky headset.
I have a 4s and my son has the S3. I prefer a smaller phone but I do find the S3 better when I'm trying to read stuff on the screen. I wish my eyes weregetting better with age but that's not happening so I can see where a larger phone will have a market.
When I use the iPad it is roughly 12" from the end of my nose. If I use a keyboard it will be more like 20" to 24". For me, at that distance, a 13" Air is marginal and a +20" would be preferable. I wouldn't even consider using an iPMini at that distance. For that reason I've come to the conclusion that a keyboard isn't of much value to me. YMMV
I didn't mention SSD in my post but hat doesn't matter. The point is that Apple charges at least 3 times the retail price for flash memory, so anyone stating that other makers won't be able to match are just posting drivel.
Assuming the imbedded solar cell has the same characteristics as a regular solar cell, one the size of an iphone screen could fully charge the battery in 2 to 3 hours. Mine sits on my desk most of my working hours so I could probably get by without ever having to plug it in.