Netmarketshare "statistics" are utterly useless, unless you want to count the percentage of OS used by idiot douchebags, which I guess alot of marketers would be fine with, as they are easier marks

Netmarketshare gives their clients a javascript and tracking cookie combination tracker, so their clients can track users across any netmarketshare using websites. Their data comes from these website clients, which means that a high percentage of the sites are probably crappy douchebags, who have no qualms about such things. Netmarketshare then has lots of marketing data to sell to other idiots.

Linux users are more likely than any other OS user to run Noscript, have javascript turned off in general, not allow non whitelisted cookies, use a hosts file to block useless bandwidth wasters like netmarketshare (their web analytic url hitslink.com is in my hosts file) or use privoxy. This means they won't show up in netmarketshare's "analysis". To add to that, are the larger number of linux user who change their useragent string, than other OS users.