Of course they are. Internal drives in a PC are removable, as well. People do not ordinarily pick them up and move them around the house - or the city - on a daily basis, however. Most NAS systems I have seen have decent cooling. Admittedly some very low end ones do not. I have seen some truly abysmal cooling in external hard drives, however. As I said, however, it is probably getting bounced around that does most external drives in.