And yes you are right that there are some of them that also have parts of both classifications, for example velvety types with a bit of tufting. They would be in BOTH.
The ones with edged cilia could be another, although in many cases the leaves are still satin except for the edges. Am not sure where I would put the ciliosums. They aren't really cobwebs but they certainly have hair. Last year I did a cross of ciliosum from Ali Botusch X arachnoideum and the one surviving seedling is a total FUZZ BALL.
I would add one more category for "oddly formed" rosettes that would include things like 'Oddity', 'Weirdo', and 'Fuzzy Wuzzy' that are distinctive for rosette form.
Like any classification system, the plants don't know they have to sit in the neat little pigeonholes that we have made for them! However, I do think it is a useful buying guide for gardeners as they might prefer one type or another. Also the velvety ones tend to rot more easily in warmer, wetter climates so you might avoid them entirely if you lived in those climates.
Kevin
