I found the reference to one third of US counites using oblique imagery in a local news story on a new user in Minnesota:
The aerial oblique imagery services were purchased at a cost of $127,719 from Rochester, New York headquartered, Pictometry, using non-tax levy recorder fee and 911-funds budgeted prior to the new year. According to information from the company, one-third of U.S. counties now utilize the oblique imagery.
The company website puts it this way:
As a result, nearly one third of counties in the United States now rely on Pictometry solutions to ensure fair and equitable assessments and improve their internal work processes for claims communications with residents and more.