In OD&D this ("the campaign is intended to be built around the megadungeon") absolutely is the assumption, and anything else ("high level" dungeons where the "1st" level is equivalent to what would be the 5th, or 9th, or whatever, level of the main dungeon) are an exception to the general rule (the possibility of which isn't actually mentioned anywhere in the rules, but obviously such dungeons appeared in play even in this era -- the Lost Caverns of Tsojconth, the Tomb of Horrors, the Temple of the Frog, etc.).dcas said:As far as "dungeon level" is concerned, I always assumed that this more-or-less scaled to the PCs' level, so that high-level PCs were not having 1st-level encounters when they entered the 1st level of a dungeon. If my assumption is wrong, it almost seems as if the campaign is intended to be built around the megadungeon (like Castle Greyhawk) rather than varying challenges and locales.
This notion appears in vestigial form in AD&D (in the dungeon random encounter tables in the DMG) but it's pretty clear that by the time of AD&D Gygax was moving away from the campaign-dungeon model (no wonder -- he'd been playing in that style for 7 years and was probably ready for a change) and was emphasizing a different approach with more focus on wilderness, town, and other-planar adventuring and multiple smaller and more cohesive "lair-dungeons" (i.e. modules) in place of the single massive campaign-dungeon.