Like Woods, Federer and Williams have arrived at the "win a major or bust" phase of their careers. Accumulating trophies for anything other than Slams seems hallow.
On Sunday, Federer defeated Novak Djokovic 6-3, 7-5 to win his seventh Dubai Duty Free Tennis Championship. The victory over Djokovic warmed the hearts of Federer fans. Federer walked away with a check for $505,000 and another boat-like trophy he'll have to find space for.
Meanwhile, his last Grand Slam win was at Wimbledon in 2012.
Williams won a record seventh title in Miami last year. She is playing at Indian Wells for the first time in 14 years. She's using that tournament to raise money for charity.
Federer has won 84 singles titles, including 17 Grand Slams and eight doubles titles. Williams has won 65 singles titles, including 19 Grand Slams and 22 doubles titles. She won 12 Slam titles in doubles and two in mixed doubles, both with Max Mirnyi.
They must have massive trophy rooms.
After winning none-Slam tournaments, they say the right things, such as "It's an honor. I'm so thrilled. This is my favorite tournament."
You just have to wonder, deep down, just how excited are they, really?
Federer has already won more Slams than any man in the Open era. Williams has one more Slams than any American, male or female. She is three away from tying Steffi Graf for most by a woman in an the open era.
Born about a month apart, Federer and Williams are in that rarefied air reserved for those who reach legendary status before they retire.
They are both 33 and in the latter stages of their careers. Yet retirement seems far from imminent. Instead, they are on an indefinite farewell tour.
Fans flock to see them. They dazzle crowds whenever they take the court and some of their best matches are played away from the Slams.
Williams' three-setter against Caroline Wozniacki at the 2014 WTA Tour Championships was far better than the match they played in the U.S. Open final. Yet had Williams lost the U.S. Open, she would have considered her season a failure. That's even with a year-end championship title.
Still, no matter how many tournament wins Federer and Williams rack up, their seasons are measured by whether they win Grand Slams.
Besides winning more Slams, what could possibly be on their tennis-tour bucket list?
Helping the Swiss team win its first Davis Cup title was among the biggest none-Slam accomplishments for Federer. He's won a silver medal in singles and gold in doubles (with Stan Wawrinka) in the Olympics.
Williams has won Olympic gold in singles and doubles. However, she has said she would like to compete in the 2016 Olympics in Rio.
Outside of Olympic aspirations, what else, besides more Slams, motivates these two to keep playing?
When Woods recently announced that he would take time off the PGA Tour, the biggest question was would he be back in time for the Masters? When you enter Greatest of All Time territory, winning majors is all that matters.
Unlike Woods, Federer and Williams are playing well. She is ranked No. 1 and he is ranked No. 2.
Both have talked about reducing the number of tournaments they play. It makes sense to focus on the Slams. Because when tennis legends are remembered, nobody recounts how many Rogers Cups they won.
It's all about the Slams.