I read through the UC-Davis Olive Center's summary report (not the 207 pages of supporting lab data; I'm just not that dedicated)--it's not necessarily a matter of intentional fraud via tampering or selling oil that starts out at lower quality as extra virgin. The authors concluded it mostly was a matter of degradation, probably through poor shipping and storage conditions (exposure to light and heat) and sitting for months on store shelves. I put a link to the report on my blog (slowfoodfast.wordpress.com)
If you look at the assay results tables, you first of all that all the downgrading from extravirgin or virgin was based primarily on the human sensory panel taste/odor/texture/appearance tests. The International Olive Council laboratory assay criteria were met for most of the oils and most of the component assays, with only a few components outside the acceptable range. If you relied on the chemical tests alone, most of those oils would have passed as extra virgin. If there had been serious tampering, you'd expect most of them to have more results outside the acceptable ranges for oxidation breakdown products, etc.
On the other hand, it could be that the IOC standards are intentionally set low. The point of the paper was that the IOC standards, which the USDA is set to adopt, don't really flag the taste and quality differences between extra virgin and virgin very well compared with a couple of newer assays from Germany and Australia. Since the cost difference in the US makes it profitable to qualify as extra virgin, that might be something worth talking about, especially as the majority of what's available across the US is imported. The California industry's not big enough to distribute nationally. But do you really need top-grade extra virgin olive oil for every dish? We ourselves may have gotten too refined.