C5 used to take it off in the summer as well though and hence remained about three months behind, though I think this year they left it on air so combined with the Olympic break they were catching up but with Seven not airing the season finale till next week they're back to where they were - current episodes aren't due to air till March.
The fact that Seven are still airing it shows how less important it is to them now - the Australian "ratings season" ends in November and it's usually all summer filler until February, with Home and Away traditionally airing it's finale at the end of the ratings season. Now though episodes have been allowed to stock pile up and they're basically burning them off in double and triple bills. That sort of scheduling makes same day airing tricky for C5, but I don't think there is a need to be three months behind.
From what I was told by an old source, the contract to Home and Away was renegotiated to cut costs during the start of the Richard Desmond years which included a clause where the programme needed to be aired a minimum of 6 weeks behind the Australian airings. I also believe the renegotiated deal included less repeats and shorter timescales for on demand showings (maybe this is why we don't get the 5star repeats anymore).
So doesn't need to be 3 months behind but with the seven networks inconsistent broadcasts, perhaps to carry on airing the show at the moment would risk going over the 6 weeks contractually allowed.