You know I've sort of
You know I've sort of wondered the same thing. I've not had the terrible injuries that you've had, but I've had lots of minor ones. Shin splints for the longest time (when I was in shoes), followed by some terrible PTT like thing in one ankle, then the other, then a stress fracture/reaction thingy in one foot, then tendonidis in the other. I've had weeks where I had problems with my knees enough to have to wear braces (also while I was in shoes). But everytime I get a injury or maybe the better word is, severe weakness that causes me not to run so it doesn't become a full blown injury, once it heals it never comes back.
I've often wondered if some of these "injuries" are more like some massive remodeling of your muscles, tendons ect... that are nearly inevitable. I think this especially since one side of me will have something wrong with it (say my knee or foot ect....) and I'll take it easy to let it heal, and the second it heals the other exact same thing will end up hurt on the other other side. Now tell me, why when I was resting to let the one side heal, would the other not have completely healed any encroaching niggles and prevented me from injuries?
It doesn't make any sense and frustrated me for quite some time. Even the minor ones stopped me from running for long enough to anger me and it doubly angered me when the time was doubled for the other side being hurt. In any case its rather odd to say the least.