If any of them do, they're idiots or they have idiot accountants. The amount of money they spend training, traveling, etc. is deductible against the value of the award as a business expense--anything they spent in the "production of the income" is deductible.
Besides, the scare story that an Olympian might owe $9000 in taxes on a gold medal is only true for an Olympian who (a) didn't incur enough business expenses to offset the value, and (ii) made over $388,350 in 2012 to be taxed at the highest rate of 35% that they used in coming up with the $9000 headline.
I think it's a waste of time carving out a tax exemption for something the IRS itself has said it's hard to imagine anyone actually having to pay.