And anything else you can find that registers with the kernel for file system calls. Logging mechanisms, etc. Anything the kernel has to talk to about file i/o is going to slow it down.
I have found Windows a bit slower but never to the extent the author suggests. But then I have generally tested on clean systems without antivirus. So I suspect that this is a huge factor, esp. because it intercepts all FS calls and checks them. That's really not what you want when compiling code.