Google maps is an example of “more is better.” Superimpose traffic and satellite images onto a regular map and you've really got something.
The same cannot be said about the profusion of style manuals at the editor's disposal—disposal being the operative word for many editors.
When an editor begins his first job, he might be expected to apply AP, GPO, AMA, or the Chicago style manual. Simple. Just learn one set of style rules and edit accordingly.
Subsequent jobs, however, will have different house styles, based on another style manual or a hybrid style derived from a particular manual (or manuals) plus house/writer/editor preferences.
Eventually, and with more and more experience, most editors want to simply cobble together their own approach to style, drawing on what they consider the best of what they've previously used, as well as their personal preferences.
Attempting to keep track of the countless—and often nonsensical—differences among style manuals can reduce even seasoned editors to bumbling novices, trying to remember where at the moment they’re working.