Interviews are a drag, and none of them like hearing that it will take one month to become fully accustomed (in-depth knowledge) with their framework. They'd prefer someone with limited knowledge who knows their framework rather than one who's well versed in multiple frameworks/languages.
It seems to me that a better approach would be to put new hires into code maintenance first with a mentor who can help them get up to speed.....
But most of us know that HR departments are not always the best judges of talent.
Programmers who advertise themselves as "Ruby programmers" or "Python hackers" or what-have-you come off as inexperienced and one dimensional. The best hackers have used the right tool for the task at and, and the best hackers have solved a wide variety of problems to require different tools.
Finally I have committed what might sound like the ultimate sin and given in to the Java/Spring framework. I'm learning various aspects of Spring, should have a small project up on github and plan on "specializing" in this framework for good.
All my other fun work is going to be done on my time alone. I look at it as the 'get serious, time to separate work and play.'