Yeah, I suspect pretty strongly postgres was built from source and initdb run by hand, because I'm pretty sure any recent debian packages would run initdb with utf8 as default encoding. Also recent debians and ubuntus are utf-8 from the start. Or, maybe it's an old installation? I'm also not so sure env vars are allowed to be influential to a package install; instead the language and other settings are stored in a config file using the debconf mechanism.
-Jim