One reason that interviewers ask the same question to many candidates (i.e., seem to have a "pet" problem) is because they have calibrated the question. A strong interviewer has asked that question to respected colleagues at various levels, and many tens or even hundreds of candidates. He knows all the ins-and-outs of the question, and more importantly, knows how to judge someone's effectiveness in that topic area based on their answers.
If you asked a different question to every candidate you interviewed, it would be very difficult to get a sense of how they compare to other candidates, or to employees.
Maybe every company is unhappy with built-in string searching operations... :-)
It's a rite of passage I think. Programming interviews remind me of rushing for fraternities in college. And once you get to the on-site, the hazing begins...
They probably ask questions similar to the ones that they were asked... so over time they select people more and more similar to themselves and their culture becomes homogenous and inbred.
What would happen if you just refused to answer the question and asked them for something more practical that would actually demonstrate your skill & experience level?
If you asked a different question to every candidate you interviewed, it would be very difficult to get a sense of how they compare to other candidates, or to employees.