While perhaps not intentional, this is a great illustration of why RDMBS are so great for general purpose data storage. If your data have fields like "birthdate" and "last_name" and you need to be able to do quick retrievals based on equality or ranges of those values, use a relational database. They've had indexing and index maintenance figured out for decades.
That thought did cross my mind while I was writing it. Indexes give you the ability to do ad hoc querying, but they have a tremendous cost to them, at least in terms of the complexity that they add to the database. Part of the point (since I don't actually work on Riak) is to point out what RDBMSes give you out of the box.
