I am bit confused that a tax specialist concluded something like that. In the end it's like a tooth paste manufacturer would have to invoice every buyer who buys the tooth paste in a store that the manufacturer supplies the tooth paste to. I think that does not make any sense does it?
Anyways I think you should be contacting your local government tax office in the end they are the ones that will want explanations if you should be audited or something.
As I mentioned in the other thread I contacted my local tax office because I wanted to have everything cristal clear (mind this was for work via oDesk, but I think essentially the same financial flow as here on Envato) and after quite a long conversation I was reassured that if I invoice oDesk everything will be allright from the TAX point of view.
Also if you look at the cash flow Envato invoices the full price to end buyer then they take the fee which is their income and the rest goes to the author which is their expense. So if you invoice Envato once a month for all the fees you receive your are not withholding any income are you? If you would be audited you can always show your Envato account to the auditor so they see that any money you receive is all on the invoice. I guess any items are digital goods and any fees from referrals would be a service I guess.
Once you know you only have to invoice Envato and you know Envato is in Australia then everything is clear you just charge the total amount and don't charge any VAT because Australia is outside the EU. And that's it.
Again contact you local government tax office for clarification that the best way to get reassured I guess.