do you mean they hit a lot flatter? (not a sarcastic question)
it seems the courts are slower, which is necessary because otherwise with current player fitness/power levels and the strings there wouldn't be ANY rallies EVER.
clearly tennis has evolved as all other athletic sports have in terms of players' fitness and conditioning. there's the odd freakish figure from the past, like Borg, in every sport, but essentially the changes in racquet technology, balls, and court speed are used by fans of yesteryear as a cloak for their arguments that players used to be better than they are now, contradicting the progression made in pretty much every single athletic sport in the last 30-40 years.
the game is clearly faster even than a decade ago, though it's a shame to see the French Open now apparently getting quicker and merging with the other surfaces too. the ball might move off the surface at wimbledon quicker 30 years ago, but it sure didn't go through the air as fast. the average top player's all-around abilities and shotmaking and athleticism are off the chart compared with 20 years ago.