Now… sometimes you have some tools on your team… but that’s another article. 
I must confess that I’m writing this from the perspective of a guy who has invested a lot of time into a specific technology, and is now having a difficult time getting work in that specialization. So take what I’m about to say from that context.
Perhaps a bit idealistic of me here, but why don’t more companies focus on forming great teams with the people that they hire rather than focusing only on hiring for a specific tool? Do you hire the carpenter, or do you hire Ryobi, Craftsman, Stanley, and Makita? Maybe it’s a symptom of the ‘keyword frenzy’ … this long list of acronyms that recruiters and hiring managers are tasked with attaching to the jobs they have open. Maybe they think it is more difficult than it really is for a good developer to transition from one language to another.
I would think it would make sense to hire someone on your team who is a strong Sr. level developer in one technology as a Jr. level developer in another and then train them the way that you want them to be trained. This spirit of ‘Apprenticeship’ is surprisingly lacking in this field, particularly considering the open source movement. I would totally be willing to take a pay cut for 6 months to a year if it meant working on a team with a technology that I haven’t used before, or one that I wanted to gain more confidence in.
I know what you’re going to say… why not hire BOTH for great teams AND the tools you need? And you might be right… but let’s say that it takes an otherwise good developer 3 months to ‘ramp up’ with a specific technology. Now you have a guy who is essentially a Sr. level developer with strong OO abilities working in a Jr. level position for at least another 9 months. They are happy to be working, learning something new, adding to their toolbox… and so long as you are able to promote them as a Sr. within a year, they are probably going to be loyal. You’re going to have a 3 month ramp time regardless. Even if you have a developer who is already proficient in the technology you’ve employed, they are going to need to learn your own unique way of doing things. The kind of developer who would take on a position like that is probably the type who loves what they do, and will work overtime from home in order to get better at it, so you basically get double the hours from them at least in the beginning. The developer’s interest level in the technology is now based on the excitement of learning new things about it. You’re not likely to get that kind of commitment from a guy who has been developing in the same language for a decade.
Really my point is that in technology, tools change… sometimes frequently. Hiring for great teams makes it possible for you to move between tools while still maintaining your culture. If you hire for tools, that is all you get.