Everybody is missing the point of this entire article.
First off the main point is to show off a very well-designed iWatch concept. I'm very impressed with the guy's work and while I have a few critiques/changes/ideas to add in, it's overall very well done.
As far as the arm band, it's not supposed to show off design, but rather how the screen size would look on the wrist.
Come on guys, it's not that difficult.