From what I understand, the advance(s) in manufacture have been largely geared toward making a stronger, longer lasting, and cheaper-to-make product. The reasons for stronger and longer lasting are warranty claims. The more warranty claims you can eliminate, the more profit. And, the better material you use, the less expense goes into manufacture which means more profit as well.
The way this has been done, again according to what I've been told, is to use more material (graphte, kevlar, titanium, whatever) and less resin. It seems that over time and due to temperature extremes and restringing, the resin breaks down considerably faster than the material. This results in a "de-bonding" in the frame which leads to structural deficiences. By eliminating as much of the resin as possible, the product lasts longer and can be abused without failure, or as much.
Likewise, if the manufacturer can use less material, i.e. graphite, in the construction because it is stronger, then they can produce frames at less cost. The weighting of the frame then occurs using something other than material and can be done more to a spec which produces a more consistent product.
I can say from experience that the racquets are considerably better than they were to begin with. I remember breaking 3 or 4 Yamaha YFG50's during play over a two year period. That doesn't happen now. A buddy of mine and I were hitting just last week and his Head frame broke at the 3 o'clock. But that is the first time I've seen that in a long time.
The original graphite racquets were beasts. They weighed as much as wood and were balanced evenly. Trying to play with one today is a real effort. The years have seen not only a change in the material, but the construction and weighting/balancing of frames to match level. Where once there was one wood racquet for every player, now there are racquets geared toward level. I mention this only to show how much manufacture has evolved.
On the flip side of this, you have pros like James Blake who say the new material or product is "tinny" compared to what he had. Blake, in an interview, said the Dunlop had tried to replicate his old frames and couldn't. From my personal experience with the C10, I can't tell the difference. I have an old fish scale hotmelt C10 and the newer yellow/black and all-black models and they feel the same to me. Well, the fish scale does feel more flexible, but part of that can be the number of times it's been restrung. In any event, the differences are minute and don't cost me any points.
Anyways, the old school graphite rackets were much more flexible and thicker layers, not air shells. See below ref for a little more info on some of these issues:
