I personally think that "estimation" questions (sometimes called "Fermi problems" since Enrico Fermi was famous for asking them) are a great way of gauging an individuals thought process.

They aren't about getting the right answer, but rather about seeing how one breaks down a seemingly difficult question into simpler pieces and determines what can be reasonably estimated. They really don't fall into the category of "brain teasers" which involve some sort of trick.

However, the statement that software developers are not asked these types of question is not universally true, nor should it be. In and SDE interview, I was asked an estimation question that was both interesting and relevant to the position (although I signed an NDA, so I'm not going to give specifics).

In my case, there were several pieces of required information that I realized I couldn't reasonably estimate on the spot, so I gave a description of how I could ballpark them from quick measurements.