1...That's the way they usually head. Granted it can take them a while: took them 4 years to discontinue the 2012 A1278, but that machine's days were numbered as soon as the first retina Macs appeared. They kept the 'relic' going, because, once again, it was the cheapest MBP and it sold by the bucketload, loads to enterprise, with its awful 1200x800 screen with an appalling viewing angle, tinny speakers, antique (by 2016 standards) i5 processor, spinning plates of rust for storage, 2GB RAM (iirc) and a DVD drive.
2...IMO that's better than the webcam on 13" MPB, be it because of clever processing or a different module, but obviously other opinions are available
4...We'll never know but once I again I suspect it's for no other reason than it is the cheapest Mac with Pro in the name. Outside the UK, enterprise buy them by the bucketload, and one mention of better cooling to stop their knees getting burned and it's an easy upsell to gullible customers whose needs would likely be met by an MBA.
6...As 1.