But you are forgetting that its much easier to hire experienced Java programmers than experienced Scala programmers, simply because there are not that many of the latter.
Same for knowing any of {Perl, Python, Ruby} and being able to easily pick up the other. Some of the more advanced idioms may take longer to learn, but it's a fact of life that you'll have to learn new languages as you go.
On the other hand, if you need to hire average but experienced programmers (e.g., if you're doing outsourced CRUD app development) then you might have an argument.
Google would disagree. As would Microsoft (they were very interested in interviewing me, even though I've never done Windows or C# programming and made that clear on my resume), Facebook, Amazon (http://groups.google.com/group/mi.jobs/msg/d81b6c1fa8f361fc) and other serious software successes.
Sounds like you want coders, not developers. What reason would talented developers (the ones with offers from all of the above, plus start-ups competing with you) to join you?