IMO there are certain occasions/circumstances where income derived as a result of services or deeds performed as representatives and good will ambassadors of the United States, should be considered waivable with regard to taxation.
We want these athletes to be at peak performance every four years. For some, expenses for travel, equipment...etc outweigh the small stipend they receive for winning a medal anyway.
It's just nickel and diming.
The tennis player is a business. Not a person performing a service for no guaranteed or necessarily ongoing income.
The medals should be called gifts from the IOC and be non taxable.