That applied to all system memory rather than what was in use. Memory errors in regions not in use are harmless while there are plenty of places where memory errors can occur in memory that is in use where they would not be noticed. Take the buffer storing this webpage in your web browser for example. A bit flip there would cause a misrendering that might not even be noticeable. Additionally, when a program crashes or the kernel panics, users are more likely to think it was caused by a bug in the software than a bitflip. In the rare cases where something goes catastrophically wrong, they tend to blame the software too.