D20 has no lore, D&D does, which is copyrighted and thus isn't getting used.

D20 has rules for altering things so you have an idea of power levels and such, so you can alter any D20 creature however you want and still have an idea of how it will balance.

ampoliros even admitted that the units being talked about aren't carbon copies of D20 units, only that people are intimidated by the large content of D20 creatures, but seems reluctant to provide his own version.

MoM did indeed have no lore, i don't know how WoM is going to deal with lore, if at all, so far only mechanics have been discussed, and full D20 isn't going to get implemented, how much is, i am not sure.

D&D lore is weak, and generally worlds are built using their own lore and then using modified D&D rulesets (greyhawk, forgotten realms, etc.), in fact it is for the most part meant as a ruleset for balance purposes so that one can make their own lore and reasons as to why things are were they are and doing what they are doing. dungeons don't have to a series of tunnels and caves, but can be the wilderness along a coast or a city, pretty much anywhere. as for how extensive are the rules, well the have seige rules, army rules, pretty much everything except 4x economy rules (which is pretty important in a 4x game).