I agree that, in the abstract, it's inconsistent.

But in the concrete:

* Looking up some additional data for each array element is a particularly common thing to want to do.

* We can support it nicely without having to create a library of operations baked into the protocol.

I really don't want to extend the protocol with a library of operations that you're allowed to perform. It seems like that library would just keep growing and add a lot of bloat and possibly security concerns.

(But note that apps can actually do so themselves. See: https://news.ycombinator.com/item?id=45339577 )