sure, it could be added to the README that before installation the umask should be set to 0022, but if the permissions were set correctly when dumping files life would be easier for sysadmins.
It seems to me that the permissions _are_ set correctly when dumping, but not when installing the source files. Why shouldn't the user be allowed to install with umask 077 if he wants to? The README might say that the user should set his umask the way he wants it to be, but isn't that kind of obvious?