Personally I'm totally okay with expecting a code sample. The best hiring process I've been through had me writing some trivial code in the employer's favourite framework (which required me to learn the basics of that framework), and then present my code to the programmers, who would ask questions and then (by email) vote. It was not code that would be used in production, but it was a great way to look at how people worked.

In the DuckDuckGo case, it looks like it might be something that would be used in production, which would make it a bit less ethical, as it would make it technically work for free.