I daresay the reason for "how few people have reported this error" is because the vast majority of users don't know about DPReview, wouldn't have a clue how to report it here nor where to report it on the internet. At best they probably went back to the place they bought the camera from.
Your reasoning is flawed. To begin with people are far more likely to complain about an problem than declare they have none. People on DPR is a good representative sample so if you count the number of people who own Sony cameras and post in the forums and compare that number with the number of people who say they have had the error you can then get a good idea of the
percentage of people who have this error. Based on that I'd say the percentage is very small and the error is rare.
Example; If,
hypothetically, 1,000,000 Sony cameras have been sold in the last 5 years and 1000 people have had the error that is only 1/10 of 1% which makes it rare. While 1000 might seem like a lot based on the total number sold it is not.
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Tom
Look at the picture, not the pixels