In a way its normal because with SATA drives and AHCI enabled, you have the ability to hot-swap. You may think your disk as fixed and never intend to swap it. Someone else may have a swappable tray on that same controller and want it to be listed in Safely remove. In fact every SATA disk should have that capability, it would just be nice if Windows had a check box for each drive so that you could choose which ones you want to be removeable.
Basically windows is just acting on the info about drive properties it gets from the driver
and the disk. So updating the mobo drivers
, as Al suggested should do the trick. Having said that windows should be smart enough not to see the boot drive as removeable...