"And they weren't all QANTAS airplanes either. QANTAS services many international airlines in transit. i.e. How many more corroding oxy bottles are out there ticking away?"
One aircraft was serviced with nitrogen.
This from your link Belgique,
"The incident was reported to the Civil Aviation Safety Bureau, which confirmed that an investigation detected nitrogen in the crew oxygen tanks on the Boeing 747-300. A bureau spokeswoman said it was a one-off incident."