There's nothing wrong with learning to first code on Windows. If it is easy for a kid to get going and start making stuff, they have a much better chance of sticking with it long enough to actually be interested in it as a hobby or career. My first programming experience was VB6 on Windows 98. I went from there to C in Visual C++. Fast forward to today and I write Java on OSX that is deployed to Linux machines. Most…
>> CS fundamentals can be taught on any system This. I don't know why a lot of people just assume that having Windows means you'll learn using Microsoft's development tools. Nothing's preventing you from choosing Apache over IIS, or Postgresql/MySQL over SQL Server Express. Most major web app development platforms run on Windows, and there are plenty of good, free text editors too.
This isn't CS fundamentals, but, at least for a good portion of CS 1 classes taught at my school, and all of the CS 2 and data structures, Visual Studio is what people are taught, with the OS X users typically using XCode.
I don't know if it's better to start with IDEs or just basic text editors and compilers, but I know a lot of CS majors are going to be coming out of my school without knowing how to compile and run almost any program without clicking on the green run button in their IDE.