Having a Bachelor's degree in (Dutch) tax law i've been very intrigued by this same question.
Even more interesting. Property tax!
If you have say 10 AUD's no tax inspector will bother, but if you own a LA, privateer and some nice hunting gear. It does become a substantial amount.
The same if you own a few thousand shares/deeds.
As far as i see. It depends on the tax. For property tax. It doesn't matter what your intent (hobby/business/investment) is. The amount matters.
For income tax. At least in the Netherlands. The source is important. Earning money by playing a game is not deemed a source of income (but that has a subjective component too, so it will change in time). So in basis i'd say that is untaxed.
HOFs...i'd definitely say those can be seen as gambling wins.
So a simple thing as a game ccan have quite a complex and interesting side effect. Can't wait 'till the first cases are fought over these questions.!!