How about both...
I think the resurgence in Greyhawk material has been spurred on by the RPGA and its various regional campaigns. When WotC allowed this to be used for its test system (so as not to upset their more popular settings) they had no clue as to the potential they were giving to a Greyhawk resurgence. I think it was only after the cat had escaped the bag that they realized that they had doomed their plans to jump the setting to a more established setting like FR.
Of course, since it was the default world, a lot of folks decided to actually research it and low and behold, all the classic setting began to re-surface. Oops, now they had to support it. Unfortunately, the writing, editing, marketing, etc, passed the window of opportunity and coincided with the launch window of 4e. The result, 4e is announced and a glut of Grehawk stuff is released as the setting is being shut down.
Its no secret that WotC wants to distance themselves from OD&D and 1e, but the fans wanted Greyhawk and Blackmoor. They gave it to them, but now they are getting FR, whether they like it or not. FR is extremely popular and will be fine for most folks. I however, will kill any dual-wielding, good-aligned drow rangers that I see and not fret twice. Elminster, be ye warned.

(PS, I didn't like Dragonlance either.)