This means that Andy Karl will have played Phil Connors in every major production of this show. (Some US regional and foreign language non-replica productions featured a different Phil Connors.)
Australia relaxed its rules around the use of international talent in starring roles a few years ago, which is why the production is able to bring over Andy Karl (and why Owen Teale is currently appearing as Scrooge in A Christmas Carol in Melbourne). I would guess that MEAA (Media, Entertainment & Arts Alliance), the Australian version of Actors Equity, probably isn't too happy about this as it makes it harder to cast locals in key roles. Though having seen Karl in Groundhog Day in London, I have to say Melbourne is in for a treat. Karl (and with due respect to the other performers) absolutely carries the show. He's fantastic.