I think that's a bit of a weird comparison: a "typical" Linux boot on a server usually doesn't involve bringing up a GUI, while on Windows you're always bringing the GUI up (right? I haven't touched Windows in years; maybe new Windows Server versions have a true headless option?). If you were to bring up X11 with a full-featured desktop environment on a Linux server, I imagine the I/O operation count would go up quite a bit.