"Editors used to hand the binders to artists and inform them that this was the “look” that character depictions should be based off of."

Do we know this for sure?  I question it for two reasons:

1. Aside from a few group shots, the guide really focuses on DC's biggest characters, and I think most artists knew what they looked like.  When George Perez was drawing Action Comics during the New 52 Era, I remember him saying in an interview "this is the first time I've needed a reference to draw Superman."  So I think if you were producing a style guide for comic artists to follow, it would be more useful to focus on more obscure characters.  For Superman, you could just tell them to check out the 30+ years of Curt Swan art that is already available to them.

2.  Other than maintaining the accuracy of some costume details, ie the WW instead of the eagle on Wonder Woman's chestplate, this isn't very useful for defining the way the characters should look in the comics, because in several cases, this isn't how you'd want them to look.  The best example is Batman.  A smiling, brightly colored Batman doesn't reflect the type of character who would strike fear in the hearts of the underworld.  This is a very well drawn Batman, but its not the Dark Knight.  These look more like model sheets for a cartoon than for a comic book.  This is how the characters would be drawn on valentine's day cards, and advertisements.  So its always seemed to me that advertisers, rather than comic artists, were the intended audience for this work.

This is in no way a knock on Jose.  Despite what it is, almost every piece is absolutely stunning.  If the style guide was made available for purchase (especially the 2011 edition with more modern coloring) I would buy it in an instant.

We'll have to disagree on this. I think he nailed what was 'on model' for the character in 1982.

(And I'd argue it was more in line with what the character should be than the darker pyscho Batman stuff that took over at the end of the 80s). 

Also, Fred's comment was that 3 generations of artists were given copies of the guide as a reference, so when I responded I was considering a longer period of time.  By the mid 80s, and certainly by the early 90s Batman was wearing a darker blue, similar to the picture Peter posted.