#3 Why? It nicely indicates the performance of both players. True, sometimes it's not so accurate, but it's a pretty good indicator. The thing which is rather not accurate are game ratings. But that is another topic.
#4. You can win with fools mate and get 100%. But is that because you played well or your opponent played poorly? And how many here focus on what they need to work on to become better as opposed to how many focus on how high the accuracy is?