The peloton didn't slow down, they were only 3 miles in so wouldn't do in such circumstances anyway. When a GC contender in a team suffers such a mishap at least one(sometimes 2) domestique will stay with him and pace him back to the peloton, it's general practice and is no big drama. The only time the peloton waits is when someone has suffered a 'mechanical', it's a gentlemans agreement they have amongst the teams/riders, an esprit de corps if you will.
As for injuries, how do you suggest they treat them? Put him in an ambulance, dress his wounds then send him back out at the rear of the peloton? It's generally accepted that injuries are treated in this manner and are fully sanctioned by the race commisars.
They don't act like footballers, they ride on whilst being treated. They hang on to the car because it's rather difficult to apply a dressing/bandage to a leg whilst it's in motion!!