Considering it is a free update, does it honestly matter what version number it carries? Bugs not withstanding, it kind of makes sense that as time progresses, iOS updates will become more of a refinement than a laundry list of outright changes. Increasing the version number is really just marketing and since that marketing isn't for a paid product, who cares?
It also doesn't help that Apple is on a yearly release schedule for major OS versions. Since they are scheduled, it only adds credence to the idea that some releases won't be a earth shattering as others. They really need to release new versions when there are enough features available to call for it.