Christian, I can totally agree with your statements. Maffetone (as I am informed) made his observations with steady state cardio (running). To classify S&S I would define it as Interval training. Looking at my hr graph after a session I have 20 spikes and 19 valleys. Trying to beat the clock makes it a HIIT, in my opinion. And yes, Maffetone is one method to stay aerobically, and I think it fits nicely because with it everyone has a valuable cue here to use the right weight, reps, sets and rest times with it, regarding S&S. I may be wrong here: another (maybe scientifically and individually correct) method would be Spiroergometrie in a lab while doing swings and get ups, or lactate testing. But the Maffetone seems to be a very usable hint for a lot, maybe for all people.
S&S is not written in stone either. It contains many hints and cues to train properly, and it is not the end of all means. Heck, even the exercises can be changed, when Pavel Macek makes his fighter use sometimes push presses instead of get ups. But I think, and here is the key: S&S is about principles, and these are written in stone. But they are no dogma. The thing is detect the principles and act/practice accordingly. The principles come out of experience from many human beings, thus out of live itself. These principles are valid for a human being, past, present and future. Androids and ego have other "principles". Another statement about S&S could be: practice mindfully with patience often and regularly in your zone and grow like grass almost all by itself.
To make this practice permanent everyone is (and should be) free to making his or her own adjustments as I said the weight, the sets, the reps, the hr for those with a hr-monitor, the talk test and then some more resting for those without, the trainingfrequency. Make your practice repeatable to stay with it.
Currently I am using the beast. I am elaborating my starting hr. For my first sessions starting last Saturday (204th session) my starting hr was 100, and my highest hr was almost 150 (142 Maffetone, + - 5bpm). The sessions felt very good, but after three days some fatigue built up . Yesterday I let my hr down to almost 90, my max was 139. It felt exceptionally well, my sleep was well, although my training was somewhat late in the evening and woke up this morning rested. As I said somewhere earlier, a lot of tinkering here, and I want to see which impact it has on my traininfrequency. So, I am just tinkering...
And by the way, the practice of zazen and practice of S&S with it's focus on attitude, posture, "egolessnes" and permanence have many things in common. This would make up a nice other thread.