It's not just about screening people for already knowing the tools. It's also about finding people interested in learning or using them. For instance, I'd imagi

It's not just about screening people for already knowing the tools. It's also about finding people interested in learning or using them. For instance, I'd imagine it's really difficult to recruit developers willing to work on software built in Cold Fusion if it's not already their preferred language. The same goes for anything new and sufficiently obscure. That limits your hiring pool significantly. And for the newer ones means you're unlikely to be able to find anyone with a deep understanding of your language or framework (or DBMS)'s internals.