I've never heard of "pitch up" and certainly never experienced it. Perhaps I've just not noticed, but if a guitar was a semitone sharp after storage, I would have thought I would have noticed by now! The Fender article does not refer to this phenomenon either as the reason for tuning down for storage, but doesn't mean to say it's not the reason. Are there any other sources that back this up as I will downtune my guitars if there is actually a risk to them! I've never had neck issues with any guitar I've ever owned but would like to avoid them too.