I just heard back from Doug Carpenter, and here is his reply regarding my question:

Yes, but not because of breakdown of oil, but due to contamination of other higher flash point liquids. Approximately 0.5% to 3% w/w petrol is normally present in waste motor oil by virtue of the way in which an internal combustion engine functions. This causes the flash point, when measured by the equilibrium method (ISO 1523: ‘Determination of flash point - Closed cup equilibrium method’, using an approved cup such as the Abel Cup), to fall from well in excess of 110 degrees C for unused oil, to 70 degrees C.

The equilibrium flash point of the used oil involved in an explosion in the UK, was found to be approximately 36 degrees C, the oil having an estimated petrol content of 1.4% w/w. During reprocessing, the oil had been heated to approximately 70-80 degrees C, filtered and centrifuged. Oil can also become contaminated with petrol for other reasons, including; 1) The disposal of either unwanted petrol from work on car fuel tanks or petrol used to wash oily components; or 2) The disposal of unwanted fuel from vehicles where petrol and diesel have been mixed accidentally.

I am not aware of any tests on motor oil with 3000 miles that has been tested and compared to fresh oil.

Here is some data I found for different grades of AMSOIL (Synthetic), new and used. It shows a similar relationship for most oil grades.

[www.atis.net]