Protective stockings = sleeves = leggings. Same thing. But I think your 2nd statement is right. They didn't ban them outright. I think they banned them if you didn't have a legitimate medical need for them. Players like TMAC, Kobe, Wade, and Iverson were kind of wearing them as fashion statements and the NBA didn't like that. If you really need to wear one, that's fine. But if you wear one just because you like the way it looks, then that's not allowed.
As I said, I would approve of Yao wearing them for sure. I think the only reason why he doesn't is because of comfort... I mean if you think about it a lot of players like old T-Mac would wear a lot of sleeves for no reason, like his calf sleeve and his elbow band but that's because he was comfortable with it. Those of you who have played basketball know that it can take time to adapt to new sleevings and pads. It doesn't take that long to adapt, but it can be uncomfortable.
Everyone likes that look. Should have never changed from those unis. Yao needs to go Rec-specs, wristbands, and padded up like Biggio.
I'm not so sure its so much comfortable as it mentally throws you off your routine. A lot of athletes have specific routines and things they do to prepare or during a game that are almost ritualistic in nature like taping your fingers in a certain way. I'm just guessing but I'm guessing for Yao wearing a knee pad just throws off his routine.
Compression pants and shirts are more than a fashion statement. I started wearing Under Armor compression shirts and shorts a few years ago and will wear them whenever I'm doing something athletic whether it be martial arts, skiing or running. Stuff like that does three things. First is it helps pull moisture away from the body and it feels as good and sometimes better than just relying on bare skin to cool. The second is it prevents chafing and abrasions. The third reason is that the compression on the joints and muscles feels is much more comfortable during strenous movement than without. I've injured every major joint in my body, some multiple times, and there are days when if I wasn't wearing Under Armor I think I would have a tough time even moving.