Secret Doors and Puzzles in D&D

Big Purple has a discussion of this going but other than the reappearance of Old Geezer (the young fella at Gygax's table and a RPG.net legend) its not an exciting discussion.

My impression of secret doors and puzzle traps and all that is simple

These serve much the same purpose as unlockable content and puzzles do in computer games. Its a reward/another thing to do if you play it over again (with another group or by returning to the area later) or if you are clever about it.