You don't seem to understand how stored views work. This computation cost is felt at insertion time and is not theoretically worse than the exact same computation cost at insertion time in a rdbms to build almost identical index structures.
What current implementations of rdbms's gain you is the ability to write completely ad-hoc queries and get reasonable performance most of the time. This is an implementation advantage, not a theoretical advantage.
I understand that you can have indexes -- which, in my opinion, seems to defeat the purpose of NoSQL in the first place. You take your unstructured data store and structure it.
Also, in the authors example the items are properties of the order. How exactly would you index on those?
What current implementations of rdbms's gain you is the ability to write completely ad-hoc queries and get reasonable performance most of the time. This is an implementation advantage, not a theoretical advantage.