I've noticed many examples (ST 2.1 RC2) that use Ext.data.JsonStore. But it doesn't show up in the help under the data tree on the left. And when I did get to it (via Store's subclasses section), I found a big pink notice:
NOTE This is a private utility class for internal use by the framework. Don't rely on its existence.

Should the examples really be using this if we're not supposed to? Isn't it a bad thing to teach?

Some topics with examples that use it:
Ext.chart.axis.Category/Numeric/Time (lots of examples in charts particularly - probably a lot of them just copy/pasted)

In the exampes:

It's also just kind of weird that JsonStore is marked as private but not its siblings ArrayStore, DirectStore, or NodeStore.