Bullshit. The only reason why people ask these things is because big software houses do so, and for some reason they think that their shitty web app needs a Google quality "rockstar developer".

The difference between reversing a string and pulling data from a database are, literally, completely different tasks. The killer is that the latter is something that a candidate will do in a job.

You're more than welcome to ask those questions, and you're probably likely to weed out the lowest common denominator types. In my experience, they're a waste of time and the best possible interview you can give to a developer is a frank face-to-face discussion about programming, and then getting them to work on a test project for two hours from your own code base. If they can do that much they can program.