A couple of reasons that I'd guess at.
1. Ken is an avid fisherman and there was a book written by Izaac Walton called The Compleat Angler in 1653 compleat began life as an archaic form of the word "complete", but came to be used for the specific meaning below.
2. Compleat is a real word, meaning highly proficient.
3. The common adjective "complete," has many meanings, only one of which is "proficient"; others include "having all parts", "concluded", "thorough", "absolute", etc.
4. It's not unusual on the web: the last time I checked, over several thousand Web pages were also using the word (though often incorrectly, as a synonym for some other meaning of "complete").
Hope that helps,
Oskaar