Apple is not exactly to blame here. That diagram is posted on their developer pages and is thus first meant for developers. What do developers care about? The App Store and its users. They dont care about those millions of users that are not represented on this diagram, because these are not their potential customers. The fault lies with those who treat the diagram as a proxy for overall adoption of iOS versions, which was not the data Apple intended to show.
Very valid point. And one I am sure most overlooked.