Curiousv:
Weight is not a good measure for this.
(and pretty much everything else)
These are great points, especially for people who don't like to focus on numbers. A lot of people (like me) love seeing the numbers go up, but for others it's the growth, adaptations, outgrowing, etc., and the numbers distract from that or make it less enjoyable.
I would also suggest there is an attitude difference between the body types, as well. A BBW/BHM gained weight and doesn't really want to grow any more because of their lifestyle but they still feel sexy and don't really want to increase activity. An SSBBW/SSBHM might be someone who feels much more attractive and happy the larger they get, although they have hard limits they won't exceed. A USSBBW/USSBHM wouldn't be a person who either has a medical condition or is part of the feedism community and has either grown to the point they are significantly limited in daily activities and likely would not be able to change if they wanted to (which they don't).
So yeah, I think mindset matters, too.