True, I didn't look at it that way. It seems more likely that that's correct -- "Why those exact five?" -- but why would Quirrell find it so amusing?
edit: Maybe Voldemort has already hidden his Horcruxes in just those manners -- we already suspect that he launched one into space. In that case the riddle may be -- given that Harry and Voldemort think in precisely the same way, how can Voldemort think of a hiding place that Harry wouldn't think of himself?
edit2: It's out of character for them to come naturally to Harry, but not to Voldemort. Voldemort is into that kind of superstitious ambiance -- e.g. he wanted precisely 7 Horcruxes, because it's a lucky number. Harry is part Voldemort, so that's why they slipped into his subconscious.
*shrug* maybe I'm grasping at straws.
Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread: