Ok that makes sense - big crowds! Are the Rugby crowds - union and league crowds effectively split what I mean is do league fans not go to union and union not to league.
It depends on what part of Australia you're in, for example in Canberra and (to a much lesser extent) Brisbane there's a fairly large crossover between RL and RU fans, but in Sydney and Melbourne the two groups are much more split.
Was wondering why such a big difference to AFL crowds - the TV would suggest same popularity. its true to say most Americans would not know there are two Rugby's.
That's basically because of geography and culture.
I don't think that anybody really knows exactly the reasons why Aussie rules supporters have been more hardcore then other football supporters in Australia, but even way back in the 1800's there's evidence of this being the case.
For whatever reason a culture of supporting your team at all costs (to the point that some fans resemble cult followers willing to believe and do almost anything that clubs and by extension the AFL says) developed in Victoria in the very early days of Aussie Rules, and as Aussie rules spread that culture spread with it.
The only reason that everywhere north of the Snowy Mountains isn't the same is because Rugby (and later Rugby League) was already well established in Sydney and Brisbane, and the distance between Melbourne and Sydney was at the time too far for the governing bodies of Aussie Rules to mange a concerted effort to push Aussie Rules in Sydney, and every attempt to setup new governing bodies in Sydney and Brisbane (as they did in Adelaide, Tasmania and Perth) ended with that body going bankrupt before successfully setting up a popular and profitable first grade competition in Sydney.
Swap the words Aussie Rules with Rugby and Sydney with Melbourne in the above paragraph and you've roughly got the reasons why Rugby didn't catch on in Melbourne, Adelaide and Perth.