I'm honestly not sure. From what I understand, anybody who uses the OGL (even if they're not using D&D's SRDs) needs to replicate the WotC copyright bits. Evil Hat does it, Paizo does it and EN World does it with Level Up too (Level Up's OGL page even includes Paizo's copyright notice, which I guess means Level Up borrows some mechanics from Pathfinder). But I honestly can't tell the reason why they have to do it. The depth of the legal discussion is above my capabilities. My last brush with law was in undergrad where I took three courses on French constitutional law, French contract law and Roman Law, and I don't think any of these would apply here!