Matt, based on my understanding (possibly quite limited), most of Easy Strength does not set out to give you a specific program, it gives you a lot of guidelines to follow and implement in your own training. It does give several examples of how to apply those "rules," and one of those examples is the 40 day program. Easy Strength has made the 40-Day Program more popular, and is sometimes used interchangeably. But, if you look at Dan John's blog you will see examples of his current training. This training follows the Easy Strength guidelines in terms of movements, loading, frequency, rep ranges etc. Most of the books is not a "one-size fits all" plan. But, if you follow the rules, and tweak the program for your needs, you will be following Easy Strength.
Geometry analogy: In this example the 40-day program is a square, and easy strength is a quadrilateral. All squares are quadrilaterals, but not all quadrilaterals are squares. So, if you follow the 40-day blueprint, you are doing an easy strength plan. Did I just make it more confusing?
This is the part where Dan arrives and tells me I have it completely backwards. But, I hope this helps.