I don't think that is a very thorough explanation of compression. No discussion of knee, attack, release, or make-up gain. Funny, the unit they are pushing does not have knee/attack/release controls. I would never own a compressor that doesn't at least have attack/release, unless it is an LA2A, or any other of a small number of high end compressors laking these parameters.
As much as it pains me to link to The Recording Project, the site does contain an excellent article, complete with audio examples of compression at work.