Lomapeso, sorry, I was playing devils advocate with a rhetorical question.
The reason they grounded the fleet was due to a component failure (step aside geasbox drive shaft) which related to a metallurgical problem created during manufacture by a RR contractor.
You are correct in your analysis of the statistical side of things though. There was a figure floating around on the odds of a multiple fail, based on the failure rate at the time. Can't remember the #, but I recall it wasn't pretty!