Reply part 2:
While I appreciate the effort the author has put into trying to simplify seamless white portraiture and in writing this article there really isn't any shortcut to high quality seamless white portraiture.
If you want to know how to properly do a white background portrait I suggest you refer to the tutorial by Zack Arias. One caution, however, to prevent light bouncing off the background from causing the edges of the subject to be overexposed keep the overexposure of the background to no more than 1 stop unless you can place the subject around 12' from the background.
Reply part 1:
The title of this article is incorrect. The examples are not high key images, they are simply seamless white background portraits, the second of which is overexposed on one side.
The correct definition of high key photographs can be found on Wikipedia.
A high-key image consists primarily of light tones, without dark shadows. A photograph or painting so composed features a diminished tonal range of primarily whites and light grays.  High key as a term used in describing paintings or photographs is related to but not the same as high-key lighting in cinema or photography.
Thank you for taking the time to put together this article. It is a good introduction to using a single light source to produce different lighting styles. I'll certainly be recommending that new photographers wanting to start doing portraiture read it.
Once you understand the light and shadow effects you can achieve with a single light source then you are well on your way to understanding all lighting. Only by understanding the light illuminates and shadows define can you master lighting. .
All lighting setups start with a single main or key light. Additional light sources are only used to modify that main or key light, i.e. to modify the light and shadows. Learning single lighting is the key to learning lighting in general.
Thanks again for a very nice article.