In my case, it actually was the bolt backing out. I think some do back out even with the newest version of the bolt because some mechanic who does not know the history does some type of front end work (timing belt, oil seal, whatever) and thinks that 130 is overkill and just get's "close". Safety wiring would have helped in my case the first time the bolt came out, but then I would have had to have been the one to wire it and therefor I would have already met the right spec.

Really that's a bit of a round about way to say I basically agree. Since all of us on here know about it, we should all check our own bolts, get the newest version, and torque it to spec. If you are really worried, then wire afterward but know it is unnecessary since my un-wired one has held for what, 60 or 70K miles so far...