In my experience, although not very large, people who only know one language do so because they stick to things in their comfort level. they are also disadvant

In my experience, although not very large, people who only know one language do so because they stick to things in their comfort level. they are also disadvantaged in environments where projects vary quite a deal. certain environments have different communities supporting them, making them better for certain tasks. an example, a ASP/ASP.NET developer (only thing) of 10+ years couldn't do something over 6 months that I did in a week. That something involved web pages, polling data through a restful interface, projecting coordinates, tweeting, and a few other moving parts.