Yep, it is based on the northern hemisphere. Generally, the football season starts from Aug to May (in Europe) so the WC is usually held on June-July.
AFAIK, Australia's bid was for June-July 2022 and if FIFA changes the date, there is talk that Football Federation Australia will ask for recompense on their bid < http://www.theguardian.com/football/2013/sep/17/world-cup-20... >.