The computer industry has been using a strange form of decimal numbering for versioning for some time now. You may remember or have heard of Windows 3.0, 3.1 then 3.11 being released for example. If you click on "Help" then "About" in most any Windows program, you'll find a very long release version number somewhere in that display that explains exactly which copy of the software you're running. These version numbers are frequently misunderstood, such as when Sony recently released firmware version 2.17 for the Playstation3. The PS3's previous version also being in the 2.1x series, there was some confusion amongst Playstation Blog readers about why major new features (such as "in-game XMB") weren't included.
What usually happens is that you get a version number like "3.4.6" or sometimes just "3.46". Sometimes a unique serial number is also stuck in there, but we'll ignore that for now. What you need to realize is this is not a standard decimal number in terms of counting. Many "number values" will be skipped in an average software project's lifetime. You'll go from 2.0 to 2.01 to 2.5 to 3.0. This is because of what the digits represent.
Major releases are characterized by the number before the decimal. When it changes, it is often to represent a major change in functionality or some other significant difference. In the case of rarely updated software, you may see a version change from 1.00 to 2.00 for example. What if the software simply underwent a cosmetic change though? You've taken a video game for example and not changed anything but added some online leaderboards. That may be represented by a minor number change -- when the first digit after the decimal changes, such as from 2.00 to 2.10. This may look like 2.0.0 to 2.1.0 but many software makers leave out the second decimal place for one reason or another.
Very minor patches such as a small bugfix with no real change in functionality are marked by a numbering change on the final digit such as 2.15 to 2.16. You may have fixed the balancing of knives versus swords in your online RPG, or added a sorting feature to those leaderboards, nothing really significant to most people. In that case the final digit is updated to show that although its a different version, is barely any different than the one before it.
Also note that you may not see these numbers in a direct sequence as update versions may never hit the public (there may be a 2.07 that was wrapped into a 2.10 release for example instead of being released on its own). You may have been ready with the aforementioned 2.16 release for adding a sort feature to the leaderboards but it turns out the company has several other bugfixes and they're going to roll them all into a 2.20 release instead.
Hopefully that makes some sense out of the issue for you, and although these aren't hard and fast rules, they are frequently true when you see a version number.