"Is material designation inside Creo a useless feature and no one uses it and that is why PTC did such a half-hearted job
providing a list?"
The converse. PTC did a half-hearted job so nobody uses it, leaving it a useless feature.
In terms of plastics I can understand part of it as the properties are highly temperature, processing, and formulation dependent. Maybe the rest is just risk aversion to avoid problems with customers depending on properties and having bad outcomes. A great use of materials has been continuously thwarted - controlling the appearance of items. PTC has continued to shoot down the idea of using materials in family tables as a means to control colors and textures.
Maybe. I'm not lucky enough to have access to maintenance, but you are. You did not comment on this thread at http://communities.ptc.com/message/234094#234094
If they are mistaken, please take the time to correct them.
FYI: PTC's official stance with colors in material appearances for family tables is: