I don't get that at all. Why? The scoring at the US Open is not different to Wimbledon as far as I know.
The U.S. Open is the only grand slam tournament that uses final set tiebreaks. Hence the marathon 5th set (16-14) between Roddick and Federer at this year's Wimbledon.
Ah I did not know that, thanks!
But the final (i.e. fifth) set is never reached in the solution. At Wimbledon it is entriely correct that you can win the match in three or four sets by winning the third or fourth set in a tie-break. There is not a problem with the solution as stated.
"Final" means the set that will end the match, not necessarily the fifth set.
It may do elsewhere but it doesn't at Wimbledon.
It was a funny reference to Federer blowing it against his final opponent at this year's US Open, despite dominating the whole tournament.