It may not have the inherent security of OS X or Linux but it's still the most secure MS OS out there.
Apple do much the same thing with moving people onti its latest OS, but very few people accuse their having ulterior motives. They both want the same thing for the same reason - as many people...
Microsoft make relatively little money from the domestic Windows market, and it makes sense to get as many people on the latest and most secure version of their OS. It's not altruism, but neither is it evil - it's pragmatism.