harold3:But... the buddy system... comments? Are my concerns valid... I don't see how teams can be so ad hoc.
Your messages indicate quite a bit of underlying anxiety. Recreational diving really is safe and fun. By the very definition of recreational diving, aven the most catastrophic gear failure can be dealt with by simply slowly swimming to the surface. Wait until you see some of the people who have safely made hundreds of dives.
Back to your actual question. From what I've seen and read, it works like this. Most recreational diving, especially warm water, high viz diving, is extremely safe. Under these conditions, divers and the training agencies just pay lip service to the buddy concept, but everyone knows they are really not necessary, so instabuddies or group diving is readily accepted and causes no real problems.
As conditions become more difficult and for all tech diving, this casual approach is no longer acceptable. But even here there are a couple of alternatives. One approach is DIR which insists on real buddy training and only diving with buddies you can trust. Another approach can be seen here http://www.njscuba.net/gear/trng_07_buddy.html (the whole site is worth a look), that emphasizes self reliance, including fully redundant air sources (i.e. pony bottle or doubles with separate regs).
I just read Jacques Cousteau's first book and came across what was probably the start of the buddy system. They all dived solo originally, but at one point, one of his divers got hooked on a wreck in a way that made it extremely difficult to extricate himself, but he could have easily been freed by another diver. He survived, but from that point on they quit doing solo technical dives.