How much income are Pro Golfers allowed to defer?

I know that the PGA has the best retirement plan in the country thanks to a sneaky special act of Congress that gave their plan a unique status. But is there no upper limit to how much can be deferred?

Tiger Woods, my golfing hero, is about to have $10,000,000 put into his tax-deferred account. As nearly as I can tell, had FedEx made the prize $100,000,000, that amount would have been put in there. The tax-free compounded money gain on deferring taxes until later are astounding.

This particular arrangement seems so egregiously disproportionate to all other retirement/pension/income-deferring limitations that I am wondering if I have it wrong…

As long as the prize-giver and the PGA management agree that a given chunk of prize money goes into the retirement fund–even if earmarked for an individual–is there no upper limit?