I think it is natural that there are many withdrawals at Toronto and Cincy this year. Preparing and playing at the Olympic (Singles & in some cases Doubles) takes a lot out of people physically and mentally. Fed's 3rd set 19-17 in the SF must have drained him enormously as he was not as sharp in the final, failing to take advantage of any of his 9 BP chances.
It is definitely bad to make Toronto a mandatory this year. The body needs time to a) recuperate b) adjust to new time zone c) adjust to the hard court surface. Without sufficient time to adjust, it is almost guaranteed to lead to injuries / loss. Andy did well to only tweak a left knee. Hopefully he will be fine comes Cincy.
I wonder why Andy didn't do a Fed and get a Doctor's note citing exhaustion after the Gold/Silver win.
I can imagine Andy's conversation with the Doctor going something along the line :
Dr. : many congratulations Andy on the fantastic win over Federer. You really showed him who is the boss now.
Andy : Thanks Doctor. I had a great time. I wonder if you can give me a note citing exhaustion for Toronto please. I have to do media service Monday and flying out on Tuesday gives me less than 1 day to recuperate and get ready for the next match. It is crazy schedule.
Dr. : sure Andy. No problem. Now which part of the body do you feel aching ?
Andy : well, everywhere really. Now there is my back that I have to keep clutching, and there are my bipartite knees, and ...
Dr. : enough. Get on the X-ray machine please Andy and I will include it in your report.
Andy : Thanks Dr.
Dr. : Here is your report. By the way, can I ask for your signature here for my niece. She is one of your fans.
Andy : of course. Anything for my fans.