I have asked the question before and receive unsatisfying answers but
here is the basic idea (please post if you find concrete examples):
InetOrgPerson is a "prototypical user" in a network environment, designed
as a NON-required RFC so that those choosing to implement it can easily
interoperate with other (LDAP) databases and have a "known" set of
attributes
with which MOST network operating systems can agree.
It's designed to give you a more open standard "user". Added when you
upgrade
the domain/forest with Win2003