WOTC, look at it this way...
The harder you make it for 3rd parties to work their IP along with your core rulebooks, the more likely they are going to make their own verison of 4.0 and compete with you instead of working to encourage D&D source book sales.
Let's say Piazo decides that they can't do their Pathfinder setting with 4.0. They could easily start a 3.75 or 4.5 type ruleset, glam it up and make it compatible with your 4.0 enough, and then pull customers back into the team who gave them dragon and dungeon without messing it up.
The company has said itself they are waiting to see whether or not they are going to do something like this. Why give them more reason to?
The harder you make it for 3rd parties to work their IP along with your core rulebooks, the more likely they are going to make their own verison of 4.0 and compete with you instead of working to encourage D&D source book sales.
Let's say Piazo decides that they can't do their Pathfinder setting with 4.0. They could easily start a 3.75 or 4.5 type ruleset, glam it up and make it compatible with your 4.0 enough, and then pull customers back into the team who gave them dragon and dungeon without messing it up.
The company has said itself they are waiting to see whether or not they are going to do something like this. Why give them more reason to?