Any Australian media website/ entity will tell you how little 'just the rating figures' matter. It's been said time and time again, these days, total people ratings are good for one thing only- adding the possibility of a show looking good in a press release. Where a show's performance counts, i.e., how a show can become profitable on a network, is in the demographics. There aren't a lot of over 55's who watch Big Brother- but there are a lot of 55s watching The X Factor. In terms of 'over 55s', networks tend to market their shows to this demographic the least. The most advertising dollars can be made targeting the three major 'under 55s' demographics and that's what Big Brother is doing and it's doing it well.
Though, it is easier to report total ratings news as that is what the general public have the most access to. With that being said, Week 2 of Big Brother averaged 820,000 officially. It should be noted that week 3 averaged that unofficially, so we should see a much higher figure this time next week!