The article (or collection of charts) is a mess. Some of its weirdness can be explained by the fact that it is measuring different things - e-reader market share in the US vs. global tablet sales, for example.
But other things make so little sense that they must be wrong:
According to this chart, about 12% of e-reader users use their e-reader to read blogs, watch movies (!), or do word processing. And something like 25% use their e-readers for web browsing.
This can't be correct - even considering a rooted NC as an e-reader, the numbers are much too high.