Well, no, the place where you play 1 out of 12 of your games wouldn't qualify as your home ground.Maybe Bulldogs should play one game at Accor and sell it out, and then play every other game at various country venues in front of 5000. Then you can claim they have an 80,000 average for the year?
The logic of excluding the various special events and neutral venues is to preserve a "truer" picture of the home crowds. Extreme example would be the first double header at the new Olympic Stadium back in 1999. If you included that 104k for the "home" teams that year their average would appear to be 7 or 8k higher than reality.