I would argue that the "two setting" notion is incorrect since currently we support Forgotten Realms, Eberron, & Dragonlance (licensed to MWP). Core D&D should be considered a setting as well just on the sheer amount of content. There is a belief that TSR in the 2nd edition days over-saturated the market with settings that split the market into to many smaller customer groups but that was with 9 plus settings. There is no belief that the rule is "2 only".
Now does that mean every setting gets a setting 300 page campaign setting book, 12 supplements a year, plus adventures? No. But there certainly is a room to provide varying levels of support.
When we have discussions about settings support Greyhawk is usually on the table.