Vacuum ignores large objects

Is there a reason why vacuum won't vacuum large objects?  AFAIK they
are not really different from ordinary relations, and could be vacuumed
the same way.  If you do a lot of lo_writes to a large object, its file
size grows without bound because of invalidated tuples, so it'd sure
be nice for LOs to be vacuumable...

Trying to force the issue doesn't work either:

lotest=> vacuum xinv150337;
NOTICE:  Vacuum: can not process index and certain system tables
VACUUM
        regards, tom lane