Hmm. Somehow I can't see the fault in his post.
The game also tells that the characters will need 13 encounters to level. To get to this number, you have to use EL = PL encounters. Yes, you can (and from experience: should) put other types of encounter in the game, but this is the baseline standard, and the game doesn't seem to recommend using the higher EL encounters.
And more to it: A EL = PL encounter reduces the party's resources by approximately 25 (or 20?) %. This means that if you want to design an encounter with many opponents at low level you will automatically reduce the amount of encounters considerably below 4-5. I don't know the example Dungeon, but I assume the designer in question didn't have in mind the party retreating after their first encounter, but wanted to have them keep on fighting.
Also note that a 50 % chance of success implies that every second time you try to make such an encounter, your group will probably be defeated or possibly dead. Not really what you want from the encounter with multiple NPCs, unless it was the climatic and final battle...