The piece suggests that audits are on the rise, but provides no evidence of this other than that audits happen. It speculates that airline financial problems have spurred more audits, but I know of no carrier that sees auditing of accounts as a meaningful new revenue source.
Instead, if audits are becoming more common it’s likely due to technology. If you don’t provide your frequent flyer number on an airline reservation at booking, and then after the flight submit the boarding passes to the airline you flew as well as their partners, the various carriers are much more likely to catch that now than they would have been in years past. Or if you start redeeming a bunch of international business class tickets all of a sudden, and they’re in a whole bunch of different names other than yours, then computers might flag this as suspicious — suggesting that you might be selling awards to a mileage broker.
The July 2003 issue of Inside Flyer carried a piece (subscription required) on mileage account audits, what kinds of activity trigger them, and how to avoid them.