its true - I was hired for a C++ on Linux job replacing PHP web stuff with C++ web services.
then I got there are found it was all C#/WPF bollocks. Fair enough, I gave it a go and it was pretty damn easy, even if WCF is a bloated heap of steaming..
But when I queried my manager about it, he said he knew a C++ dev could do the job. He was right - knowing C++ meant I knew what the intellisense-driven C# stuff was all about, how it performed and how to get the best out of it, and sort out the nasty bugs that we had in WCF (ok, it was really easy to get something working, but really tricky when you go slightly off-path).
Anyway, all those frameworks are ten a penny, any recruiter worth the job he's selling will take someone competent over someone who just knows the framework - everyone is expected to learn new stuff nowadays, so if you don't know the flavour-of-the-month framework, as long as you can demonstrate intelligence (without any belligerence regarding new stuff) then you should get the job.
But I'd get a few alternative techologies under your belt just so you can put them on the CV to pass the buzzword filters.