Is this worldwide? Or US?
Though, whenever I see these stats, the article often glosses over the single biggest reason why KK isn't much higher: the version of Android you are running on your phone is almost always out of Google's control. The only people getting their stuff from Google are Nexus device owners... everyone else has to wait for whomever made their device to get a release ready and then, in most cases, they have to wait on their carrier to accept the update, do their own fiddling with it, then push it out.
If I was a betting man, I'd wager that there is a HUGE chunk of those ICS and JB devices where the ONLY reason they are not running KK is because someone sitting at Samsung, or Huwaei, Verizon or AT&T decided they were SOL.
This kind of BS was why I got a Nexus 5.... not only can I get my stuff when it comes out, I don't have to deal with any carrier junk if I want to load something custom.... Any Verizon Wireless SIII owners who took that 4.3 JB update also got an encrypted bootloader along with it, so their completely chained to VZW.... Last I checked, VZW wasn't going to update them to KitKat.... so ALLLLLL those US customers who bought SIII's will be keeping those 4.3 numbers high until they can upgrade (starting end of this year)