39% is plenty. As OSes mature, improvements are gonna be evolutionary at best. To be able to achieve a 39% adoption rate over a relatively stable OS (XP) is pretty good. No, in fact, it's a very good result considering the bad press MS has been getting lately. I for one wouldn't consider 39% to be a failure given the quality of the product.

Extrapolating the figures given in the summary, we can assume XP has a take-up rate of 60~70%ish within the same period of introduction. That's when most computers were still running on crappy 98 mind you -- hence accounting for the greater adoption rate due to the significant upgrade.

So no, saying it is far less popular is a stretch. 19% would be far less, not 39%.