Why?
Sure, but there's a difference between "minimum rules set" and "the totality of the rules." After all, you can't say that all the supplements don't contain rules.
I don't consider the two distinct.
Neither does 5e. That's part of the whole "natural language" thing they were going for, remember? Separation of "fluff" and "mechanic" is, at best, how prior editions worked. However, I don't think you'll actually find any rules in any edition of the game that says you should intentionally ignore "fluff." I don't even know that they've ever released guidelines on interpreting rules. The closest would be the introduction to Sage Advice, which takes the same wholistic approach.