As a follow on from this, I recently went to a talk by the author and asked whether certain brands of RAM was more vulnerable than others. They said that the newer the brand (and so newer the production process), the more bits are likely to flip, but even more established brands would still have some vulnerable bits.

So it seems more of an issue with a change in acceptable tolerances - what is fine for normal usage might not be secure. Also, I might have been mistaken but the author's response implied that no brand of RAM was not vulnerable.