I don't think there is much doubt that the majority of these 'improvements' are purely just to market a new PJ. Particularly when the improvement appears to be a made up word and some of the improvements are so slight, that its hard to really notice the difference.
However, I think its different when it comes to variances. Take the new Dunlop Bio series as an example. From the reviews and feedback, these are quite a bit different to the 1st Gen Bios, which is why Dunlop also have the classic range, which appears to be 1st Gens with a new PJ. So in other words, they arent producing improvements, just variances to suit different playing styles.
Now that would be a good lead for other manufacturers to follows; bring out the new ranges with the variances, but still keep the originals (with a new PJ) for those that don't want to change.
"Tennis is just chess with balls....zugzwang"
"The older I get....the better I was"