This belief encourages fans to appreciate today's matches all the more, because a genius like Federer will likely never be seen again, and the game will be much less interesting when he retires.
However, such sentiments ought to remind us of what happened when Pete Sampras started his decline in 1998. Many of us thought no one would ever dominate the sport to that degree again because competition had grown deeper and more international, and that every year the majors would be won by four different men.
We were wrong because there was still room for the athleticism of the game to evolve, and as a result, Federer is even more dominant than Sampras had been.
In truth, no sport has completely tapped the limits of human potential, and tennis certainly has not. To envision where the sport can grow from here, one need only look up.
Starting with the Boris Becker (6-foot-3) in the mid-'80s, and continuing through the era of serve-centered players like Goran Ivanisevic (6-foot-4) and Richard Krajicek (6-foot-5), there was a fear that towering players with huge serves, booming forehands and no sense of subtlety were taking over the game.
That proved not the case when superior racket technology allowed service returns to improve to an even greater degree than the serving, and allowed rallies to last even longer.
Plus, the grass courts of Wimbledon and Queen's Club were slowed down, as were the balls the pros played with, giving players like Alexander Popp (6-foot-7) and Dick Norman (6-foot-8) no regular place to work their mischief.
Finally, and perhaps most importantly, the game's best athletes embraced the power baseliner approach. Federer, along with Rafael Nadal and Marat Safin, have since elevated this style of play to new summits.
Tall athletes (I term this use to differentiate from players like Mark Philippoussis [6-foot-4] or Ivo Karlovic [6-foot-10], for whom "athleticism" was never one of their great assets) still have the potential to dominate. Among us now, in fact, are a few such players with that potential. Safin (6-foot-4) is the pioneer.
The Russian's maiden Grand Slam title at the 2000 U.S. Open, humbling Sampras in straight sets, appeared to be rife with symbolism, like the opening chapter in a long period of dominance.
He had much of the serving power of players like Philippoussis, but unlike them he returned serve even better, moved well and could seemingly rally indefinitely.
What prevented him from following that win up with more success right away was that, he later admitted, he'd been unprepared for the pressure that followed, much like Sampras was after his 1990 U.S. Open win.
Unlike Sampras, who was committed to becoming the best tennis player of his day and age, Safin seemed driven to do little more than simply make some good money while playing the game.
It's his life, but it's a shame for tennis fans; he could have had a rivalry for the ages with Federer.
Following Safin, there have been a few other tall athletes of great potential. Most closely resembling him is the Czech Tomas Berdych (6-foot-5), who has maybe the game's biggest forehand and who can run around his backhand to hit it as well as anyone half a foot shorter.
Argentine Juan Martin del Potro (6-foot-6) was the hottest player of the summer hardcourt circuit, winning four consecutive titles and making eventual finalist Andy Murray work extremely hard to stop him at the U.S. Open quarters.
Del Potro has recently entered the top 10. What separates the other two from the top 10, if not top 5, is not physical.
Federer and Sampras, after all, were recognized for their talents even as teens; it wasn't until they learned how to control the center of the court, develop backup plans when their A-game wasn't working, and to fight for every match win they could earn that they began dominating the sport.
These are things the taller athletes have yet to learn. Del Potro, at age 20, seems to be learning the fastest and has the most time left to develop.
Both Monfils, 22, and Berdych, 23, have been known commodities for several years, but have done little damage at majors so far and Berdych has won only as many titles in his career as del Potro did this summer (Monfils has only one).
Monfils has yet to truly display knowledge of how to construct a point, and instead plays with an unpredictable flair that can be entertaining, but isn't conducive to long-term success.
As for Berdych, well, the incident two years ago in Madrid when he provoked the Spanish fans and then seemed surprised by their hostility tells us everything we need to know about his strategic gifts.
Even if none of these players develops the mind and heart of a champion, it seems only a question of when someone of their size and athleticism will.
You may never enjoy watching the tall athletes as much as you've liked watching Federer, but they'll keep the sport interesting for years to come.