No, it's 82% of the area. It's ~90.5% of the dimensional size. The post you didn't read carefully was talking about text height.
No, it isn't. Every display has a retina distance, but not all displays are retina displays because that distance exceeds the standard ergonomic distance at which it is used.
Humans naturally settle into a distance of about 30-40 degrees, which for a 17" display is somewhere around 22-24", which is inside the retina distance. It is therefore not considered a retina display.
Although it's a moot point because the OP has already tested it and found it not to be a problem, let's answer anyway. On a user interface defined in pixel dimensions, you get exactly the same amount of space. When the pixels are smaller and closer together, they're sharper, and when the display is smaller, you naturally sit more closely to it. In terms of field of view as your brain perceives it, there's very little difference.
If you position your eyes about 2" closer to the 15" screen than the 17", it appears the same size to your brain. It's quite a small correction for a supposedly much more "spacious" screen.
As explained by many people, the reason 17" laptops existed was because of the need for additional battery and electronics space and because when the best panels were ~130ppi, you had to go bigger to get higher resolutions.