I think what you posted is wrong, and contradicts reality.
Two people on the same diet and exercise plan are not going to end up with wildly different outcomes. Your words: one could be "much fatter" than the other.
Sorry, that's just wrong.
The outcomes don't have to be exactly the same, but to claim one person can be "much fatter" than another, despite their calories in and work done being the same - over anything other than a very short space of time... this contradicts reality.
Face it, you're just another of these "progressive" types who want to blame society/a.n.other for bad personal outcomes. Again I'm no example to anyone, but on matters of diet and exercise and associated body shape outcomes, I will never put responsibility on anybody but myself.
e: Just to clarify: for two people in the same diet and exercise plan, there is no way in hell that one ends up being 11 stone and one ends up being 16 stone (which qualifies as "much fatter" without going to extremes).