* iTunes gift cards regularly go on sale for 60-70% of its value on third party markets, and
* 30% is a reasonable, to cheap, price to pay for money laundering,
Gift cards would be the least efficient method here for large amounts, so I guess it would not surprise me it's not used there. No one's gonna go hunting small amounts of gift cards on discount on ebay to launder tens of millions of dollars. But who knows...