General :: Removing Write Permission Does Not Prevent Root From Writing To File

I just noticed on my Ubuntu machine (ext3 filesystem) that removing write permissions from a file does not keep root from writing to it. Is this a general rule of UNIX file permissions? Or specific to Ubuntu? Or a misconfiguration on my machine? Writing to the file fails (as expected) if I do this from my normal user account.Is this normal behavior?Is there a way to prevent root from accidentally writing to a file (Preferably using normal filesystem mechanisms, not AppArmor, etc.)

I understand that root has total control over the system and can, eg, change the permissions on any file.My question is whether currently set permissions are enforced on code running as root. The idea is the root user preventing her/himself from accidentally writing to a file. also understand that one should not be logged in as root for normal operations.