On Linux, it isn't difficult to write cool plugins in C, which can do effects that are very difficult to do otherwise. On Windows, this is extremely challenging, because getting the build environment setup is a pain. This leaves one with their Scrpt-Fu (scheme)language for plugins. While I haven't been limited by its features, the lack of a decent debugger and manual makes programming in it extremely painful (though I program in scheme (well, one of it's derivatives) nearly every day).
In one case, I found a plugin someone else had written that would do exactly what I wanted. But of course it was in C (and the compiled version only available for Linux), so I had to port it to Script-Fu before I could use it, and it took forever to run (doing pixel-by-pixel operations is very slow in Script-Fu).
Had they chosen a standard scripting language like perl/python/whatever, all plugins could be cross-platform, and would be much easier to write/debug. And don't talk about Pygimp or it's siblings. I am not aware of a single one that works with GIMP 2.2 and has been ported to windows.
The windows port is to some extent a second-class citizen, which is too bad, IMHO.
