its done with a sample, Pay TV ratings can be exact, but they tend to do it by sample as well as sample usually leads to bigger ratings.
the thing with bathurst is, it depends on how the ratings where taken. if its during 5 minute samples and they take it during half time, alot of people might switch over thus making the sample size skewed. Its a whole industry of lies and deception and is often thousands and thousands out of actual viewers.
im not sure the wallaby game will do outstanding due to the timeslot, next sunday night will be the big litmus test, 730 sunday is the prime prime prime spot for any television show in this country, the number will reflect alot on where rugby stands in this nation.