If you scroll down to the bottom of the GoSquared page, there's link to see Mavericks adoption rate. If you look at it, Mavericks went flat between May and July at approximately 50-55%, then it resumed its rise to top out in the 65-69% range.
Sales typically go flat during the summer, and go up during the fall, and especially around Christmas. Assuming new Apple systems all have Yosemite installed, it's possible their adoption might be somewhat inflated due to a holiday season blitz. Also you can't tell how many are not using Yosemite because of appearance or bugs with the OS.
Time will tell. If the Yosemite adoption rate starts going down with all the rest going up, probably Mavericks being the most likely to recover, then it would be a clear indication with dissatisfaction of the OS.