group by not returning sorted rows

I have a query:

select cities.name as city, buildings.name as building,
pagename,
log_date ,
sum(exhibition_count) as tot
from logrecords
join cities on (logrecords.city=cities.num)
join buildings on (logrecords.building=buildings.num)
where advertiser = 'Nielsens' and
log_date >= '01/01/2004' and
log_date <= '01/31/2004'
group by cities.name, buildings.name,pagename,log_date ;

I have migrated a database from a redhat 7.3 box running
[bhughes(at)compaq3 reports]$ rpm -q postgresql
postgresql-7.2.3-5.73

To a redhat 9 box running :
[bhughes(at)compaq2 reports]$ rpm -q postgresql
postgresql-7.4.2-1PGDG

and the rows resulting from the query are no longer sorted by log date.
Is this a change since 7.2x?

I can achieve the results I need by adding an order by clause identical
to the group by but this seems counter intuitive since the rows have to
be ordered anyway.

Any tips appreciated.

Bret