I've been a software engineer for 7 years, so I'm pretty sure I have a good idea what I'm talking about.
The idea is that anyone who has good critical thinking skills and can properly deconstruct a task into logical pieces can learn the "ins and outs" of any language on the fly. What does knowing how to write a bubble sort on a whiteboard with no reference materials tell you about the person other than they have memorized how to write a bubble sort? You can disagree with that all you want, but the vast majority of developers will never need to know how to do the kinds of things that are common in whiteboard interviews around the country. The creator of Ruby on Rails himself recently talked about this kind of stuff (
Programmers are confessing their coding sins to protest a broken job interview process)
Bottom line, we believe skills and experience in the under-documented or specific particulars of a language don't give any indication about how good someone is at writing software. The ability to properly organize your thoughts and work through a complex problem to arrive at a workable and maintainable solution is more important than passing some arbitrary knowledge check to inflate the egos of the interviewers.