One of the things that I think is relevant to startups hiring is that (warning experience mixed with opinion ahead) there are lots and lots of PHP developers of wildly varying quality. This makes the initial stages of recruitment time consuming. By looking for people with skills or interest in Ruby, Python or Scala (or whatever is hot that month) you'll probably see less interest but, on average, the quality and enthusiasm will probably be greater. Which means it takes less time to hire (well, maybe), as well as getting the better people (hopefully).