Their careers have paralleled so much, and now both have shown signs of being on the downhill side of their primes. I guess even a GOAT can lose motivation once he gets comfortable financially, has kids, etc.
I'd bet on Tiger to get his motivation back. Fed, not so much. He may have one more in him for New York this year, but I don't see him stretching it out much past 15 slams.
On a side note, today proves yet again why I go to the Regions-St. Jude in Memphis every year... We watched the guy who beat Fed (Berdych) play, along with Isner, Querry, Roddick and others doing well at Wimbledon. Oh, and Petra Kvitova, who's still in it on the womens side.