Usually, when a software release moves to a new single digit release, it’s a big deal. When Linus Torvalds decided to shift the Linux kernel from 3.2x it was just to make developers happy.
As Torvalds, Linux’s founder, said on his Google+ account: “So, I made noises some time ago about how I don’t want another 2.6.39 where the numbers are big enough that you can’t really distinguish them. We’re slowly getting up there again, with 3.20 being imminent, and I’m once more close to running out of fingers and toes.”