Nowadays, one strongly suspects that the writers of the D&D game do not ever play the game themselves. This is gleaned from reading scenarios shabbily thrown together, and made even more clear from rules that are entirely unworkable. Example: the dominion rules presented in the D&D Companion Game, later transcribed unaltered in the D&D Rules Cyclopedia. These rules supposedly cover managing PC and NPC strongholds and baronies, but when this DM (trustingly) implemented these rules for a group of PC barons, the result was inhuman population explosions, huge amounts of wealth flowing into the PC coffers (far more than they could figure out how to spend!), and absolutely no duties or requirements put upon the PCs to supervise or affect this stupendous economic windfall. It was patently obvious that the game designers had never sat down and actually played with these rules to see how they worked.
Contrast this (and other examples) with EGG's rigorous playtesting prior to ever publishing a scenario (or rules). Usually, in his gaming sessions, he had from one, two, or three separate adventuring groups play the adventure, and because of this he has the stories (in the module introductions) of those who have gone before, things commonly done that the DM should be prepared for, and often added depth and history by actually having the scenario reflect previous adventuring forays (particularly in regard to modules WG5 and WG6, for example).
Of course, it's self evident why EGG was the only writer to include such information, and why the "Playtest" credit quickly disappeared from credit listings. Simply put, this would be the economic pressure to get product on the shelves, regardless of contents. At least in the earliest days, EGG was mainly a gamer who occasionally sought to help other garners by publishing his own gaming successes. When the game became industrialized under the TSR giant, such concerns became unimportant. (Nowadays, authors are more likely to seek progression from D&D writing to TSR novels, and I again maintain the opinion that the two modes of writing are, in their optimal forms, polar opposites).