1) The log file will probably be used to debug problems between
clients and servers. Given the distributed nature of the Web,
the clients and servers may be in different time zones. Using
GMT might help.
2) Big computer centers that were part of a distributed network
tended to run in GMT. Of course, big computer centers are
now mainly passe.
3) Military personnel are often taught to work in GMT.
4) Isn't Iceland also on GMT? :-)
Craig Milo Rogers