That's pretty common for new language implementations - Node.js was around for a couple of years before the Windows port was ready.
To be honest, if you're targeting early adopters of a programming language Linux and Mac support is probably a lot more important than Windows. Smart Windows users can always run Linux in a VM.
It is true that a number of people do their scientific computing on Windows+Matlab or Windows+R, but that most parallel stuff is typically on linux clusters. It would be nice if julia worked on both.
It is not by design that we do not have Windows support. It's just that none of us uses windows. We do believe that code is largely portable, and with a little effort, it can be built on cygwin or mingw. Nothing like a native port though. Maybe someone who is familiar with windows will come along and contribute. This is a common question our friends and colleagues ask us.
I doubt it was intended as an insult. Julia (and other scientific languages) are often used in clustered environments, and Linux is much, much more common than Windows in HPC.