I dunno, I can't help thinking there must be a bit more background to this. I wonder what the exact content of the denial of the business visas was.
It may be they didn't provide the appropriate documentation:
Personal attributes and business background
Your personal attributes and business background must be relevant to your business activities in Australia. You may be asked to provide:
* evidence of educational or professional qualifications
* evidence of current employment and your role during your visit to Australia
* details of previous contacts with Australian business people or organisations
* documentation to show that the company you work for is an actively operating business
Examples: business registration certificate, annual report.
Purpose of visit
You may be asked to provide evidence of why you need to visit Australia on business. Evidence may include:
* a letter of invitation from the host organisation in Australia
* conference registration details
* your employment contract
* a letter from your employer stating the reasons for your visit
* your itinerary with contact details of the business parties involved.
However, unless they're expecting to get paid for the conference (and perhaps they are), I don't know why they just didn't get a standard tourist visa. Why fork out the $100 for a business one?