Did you read the article, or did you just summarise from someone else's comment on a web forum that someone had posted after reading a blog about his mate in the pub saying that ....
I just googled and the Which article I found where they tested 17 discs in December 2010 didn't say anything about the physical discs being DVDs as opposed to Blu's (as your comment implies).
They found that with some of the 17 discs tested, the picture quality wasn't significantly better than the DVD version of the film, when played on the same player & TV in a side-by-side comparison. BTW this was "man on the street" comparisons, not geek / expert analysis on DNR and grain etc AFAICT.
The reasons suggested were that some of the DVD transfers were pretty stunning in the first instance, and thus the Blu's didn't offer anything extra. Some of the Blu's were noted as being significantly better than the DVD equivalent.
And some of the Blu's were apparently a crock of shite and not worth spending any money on. I'm guessing they were ones that didn't have a proper transfer, then!