VACUUM FULL needed sometimes to prevent transaction ID wraparound?

Hello,

we're looking into the reason why we are getting warnings about
transaction ID wraparound despite a daily "vaccumdb -qaz". Someone is
claiming that VACUUM without FULL cannot reassign XIDs properly when
max_fsm_pages was set too low (it says so here too, but this is rather
old: http://www.varlena.com/GeneralBits/Tidbits/perf.html#maxfsmp). Is
this true, or do we have a different issue here? We're using 8.1.3 with
a database generated on 8.1.3 (i.e. not migrated from 7.x or anything
like that).

Thanks,
  Marinos