Um, actually, I don't that's totally true. Mostly, I think more so than string or racket technology, I think the biggest reason by far that no one tries to develop or play serve and volley these days is that they've slowed the courts down almost univerisally everywhere you go. It's quite noticeable. The 90s was in my opinion largely the era of big boy servers, all-court, attacking players, and the media complaining that the points only last like two seconds indoors and on grass. I mean you really notice watching the old masters on tape from the early 90s, I mean the ball shot through the court like lightning compared to now...AND they stayed low. A guy like Berasategui basically had NO chance whatsoever to be even *remotely* competitive when he played the masters as a result. Yes, I know he was a clay court specialist, but he was still dangerous outside clay, but at that year ending masters he was barely lucky to even put up a few games.
People may not remember, but there was A LOT of talk back then about the game being totally unfair to baseliners, that guys like Ivanisevic, Sampras, Becker, Rosset, Krajicek, Stich, etc. were ruining the game. That blah, blah, blah, points only last one or two seconds, the fans are bored, the fans want to see long-drawn out points, the fans want a rhythm to a match, it's not fair!, etc.
Fast forward, a decade plus and now they've made indoor surfaces so grainy and the grass an entirely new breed such that it's really an entirely different scenario. Now, the game favors baseliners too much, and you've got the old guard of big servers/net rushers, I think it was Rusedski, who cry no fair!-wa!-they're ruining the game!
Lol, you can't have it both ways.
With that said, I think the current conditions actually favor Federer the most. His game is such a perfect hybrid. He's a tremendous baseliner, yet with EVERYONE playing at the baseline these days, he's also got that little extra element called "all-court" tennis up his sleeves. This gives him that little extra edge to differentiate him from the host of other players with great groundies these days...i.e. a whole lot less of the middling, middle of the pack, serve and volleyers like Jason Stoltenberg and Brett Stevens and Byron Shelton and Jared Palmer types these days. Now those "types," i.e. RUN-OF-THE-MILL versions of the superstar big server and serve and volleyers of that era...have been replaced by their run-of-the mill baseliner equivalents these days.