If it was really just for marketing, they would just slap on some new stickers and change a random thing here and there with a fancy trademarked name instead of spending a ton of time and money engineering. I'm sure many of the "new, improved" things they really want to be improved, and technically it may be, but it may not improve someone's score or run out ability. In some cases, they may even have made things worse, and their older stuff becomes more desirable. I know in tennis there are some newer models that people did not like as much as older ones so there are certain model year rackets that people go after. I remember one year a brand added some extra dampening design to a model and people though it made the hit dead, everyone wanted the prior year one.
