As someone who can't stand tall-man tennis (Karlovic, Isner, Anderson, Janowicz, Raonic, etc.), I like that Chang said, "I would never say a smaller player has a disadvantage in tennis. They may not be able to hit as hard or serve as big but tennis is not all about that. Being one of the smaller players on tour, there are always ways to beat the bigger players and being smaller and quicker has its advantages. I do think a smaller player does need to be able to play different styles, though, because it keeps bigger players off balance and guessing."
This brings to mind guys like David Ferrer, Fabrice Santoro, Olivier Rochus, and of course Kei Nishikori. They've had varying amounts of success, but none of them has won a Major, and only Ferrer has made it to a final. Ferrer has won only one Masters, Santoro won a single 500 Series, Rochus has two 250s, and Nishikori has two 500s and one 250. Not exactly Hall of Fame credentials.
As much as I would like to believe Chang is correct, I can't help but think this is no longer the case. Tall-man tennis is here to stay. If anything, we'll see more and more of them. Combine that with the technology advances since Chang's days, and I don't see much of a future for guys under six feet.
I also think tennis will suffer more broadly with the influx of tall guys. It will be boring for the casual viewer to watch Isner/Karlovic-type finals, where serving is key. It's not a coincidence in this post-Sampras era that rallies are in vogue, instead of serve-and-volley. Short of raising the net, and altering the effectiveness of the serve of guys 6'5" and over, things could become quite dull.
And why not raise the net? Consider the average height of men in the 18th and 19th centuries, when tennis was being standardized. The average was around 5'5" to 5'7" -- and they decided the net should be 3' in the center.
If you use 5'6" as the average, 3' was about 54% of their height. If you take 6'6" as the average, that's only 46%. For the net to be 54%, it would need to be raised approximately 6.25" -- to about 3'6".
How would Raonic and Janowicz fair with a half-foot increase in the height of the net? It would be interesting to test it.