I'm sure a lot of other companies do this... what are some success stories?
The discussion of focusing our scope and becoming more of a single stack shop has certainly come up, and some engineers are in favor of it because it certainly has benefits. Company wide practices can easily apply to all projects, engineering resources are far easier to exchange when everyone uses the same skill set, and knowledge gains are applicable to all projects.
It's a lot harder for my custom tools I write for managing a Perl/WinForms/.NetMVC website to provide benefits for the guys downstairs working on embedded systems in c++.
Personally I prefer the variety of a polyglot shop but I can see where the appeal is to streamline company wide and specialize.
Our spread of technologies is mostly due to self motivated engineers learning new technologies and working on gaining experience to the point where we feel comfortable charging a client to develop a solution using that technology. For example, 4 years ago we'd done no mobile development. Around that time a few engineers dove into personal projects in Android and IPhone development and we've since released several products for both platforms. This was completely facilitated by employee efforts and interests. If no one wants to work on your technology stack we probably won't offer a solution and will just help you find another company.