Yes, this was true generally, due to the prevalence of faster courts and different style of play, though Rosewall was fairly physical in the day compared to others as he had a soft serve and had to depend more on his agility and energy. His volley improved with age. One could say that despite many on the tour being grinders and very physical baseliners, Federer's style of play has always been generally less physical and taxing, even on the generally slower courts of this age, than most of his chief rivals, especially lately, as he looks to serve and volley even more. I would agree that success with that strategy though is probably greatest at Wimbledon, more than any other slam venue these days, due to the higher bouncing courts that give players more time to hit successful passing shots.
Anyway, the key point I wanted to make with the Rosewall comparison was more about being able to take advantage of more decline in one's current chief adversaries than oneself, and before the future generation becomes good enough. I think a similar point can be made with Andre Agassi, who by the way, I would judge played a more physical game than Rosewall or Federer. He won 4 majors after age 29, as his chief contemporaries declined on hard courts, while players like Roddick and Federer weren't quite developed yet.
As others have mentioned, if something similar were to happen with Djokovic, Murray, and Nadal, or even 2 of 3 of those, it might become possible or very possible for Federer to take advantage, depending on how long Federer can keep his level high enough. One could certainly argue that Andy Murray has not played at a high level so far this year, despite his RG result, where he didn't defeat any player in the top 20 on his way to the semis debacle versus Nadal, and has only won a single match against a top 20 opponent all year, a poor Tsonga in Miami. He just lost in his second match at Queen's Club to 35 yr old Stepanek. Maybe Andy will improve at Wimbledon, maybe not, maybe later. Recovering from back surgery and career fulfilling success can be tricky.
Rafael Nadal just incredibly won RG for the last time in single digits. But his grass play hasn't been good since 2011. Who knows how long he will continue to do well on hard courts? Was the US Open in 2013 his last hurrah on hard courts? Even his clay court results this year prior to Roland Garros were the worst since 2004. But Rafa's decline is difficult to judge. He can be up one year and down the next, and only winning Roland Garros appears to be the constant. With enough breaks in his schedule, he might be very competitive for two or three years yet, intermittently, and one may be able to achieve more while he is at a low ebb.
Novak Djokovic is probably the toughest slow to medium hard court player at the moment, but he has struggled to win finals, and he is getting married and having a child. One doesn't know how that will affect him. If he declines sharply, I feel it will be more from mental or personal reasons than physical reasons. But he is still young enough and is the sort that if he gets on a roll could still be very dangerous as he approaches 30.
Roger isn't any spring chicken. His 2013 was his worst year since 2002, but he says that was mostly due to back problems. In 2014, he and Mirka just had twin boys to add to the other twin girls, which probably hurt his preparation for Rome and Roland Garros. But so far in 2014, he has already had a much better year in terms of performance and results. He couldn't avoid Nadal at the AO, but beat Murray, and didn't fare well against Gulbis at RG. But the rest of the year prior to the twins birth was pretty good and he just won in Halle. And he has beaten Wimbledon #1 seed Djokovic 2 of 3 times this year, a good effort against the seemingly wrist hampered Novak in Monte Carlo, playing extremely well to beat Nole and win Dubai, and almost taking the third at Indian Wells, but losing in the final set tiebreak. He lost two other finals, one in Brisbane early to friend Hewitt, and then to good friend, Davis Cup partner, and post AO win Stan Wawrinka at Monte-Carlo.
If Federer is still competitive with the best at this point, than I see his decline as staying very gradual relative to the rest barring injuries. A sharper decline by the others could make it possible, or even very possible to win more majors, until the youngsters get up to speed. But possibility and opportunity doesn't equal results. Lulls in form, upsets, and injuries can happen and thwart all. So a certain amount of good fortune is also in play.
Respectfully,
masterclass