What percentage of development shops are pigeonholing their clients by their loyal adherence to their prescribed stack? Far too many. At V-Tek, we’ve found that .NET often fits quite nicely into our mostly open-source toolbox. Especially when our client already has an MS oriented product.
Everything from raw library-less JavaScript, to RoR coding by convention, should be fair game for a development studio worth its salt. Otherwise the first thing they will want (and have to) do is uproot your existing modules. While uprooting modules may be exactly what you need, doing it only because your trusted developer doesn’t understand them is just stupid. What you already have could be ingenious, but if your developers don’t recognize genius when they see it you may well pay a lot of money only for them to downgrade your system.
One of the most powerful combinations we’ve leveraged somewhat regularly is PHP scripting routines against MSSQL systems on Windows servers. Combine the power of CLI PHP with Windows’ Task Scheduler, libraries like CURL and Sockets, and we accomplish things that other shops have flat out claimed impossible.
So unless you, as a customer, are narrow-minded, then it is best not to hire a narrow-minded development shop that will treat you like a child while they themselves waste your money.