When low is not realy low

Wow! 2.589.64 Euro is the lowest fare travelling with DELTA to Atlanta – one way! I just checked the DELTA website with its Low Fare Promise to compare offerings I received from travelocity and opodo and my travel agency. Cheapest offering for my roundtrip Berlin – Atlanta – Orlando – Munich is around 650 Euro.

I bet nobody buys tickets directly at DELTA website. The difference in pricing seems very strange to me.

Update: I understand that roundtrips are much cheaper. But what I really don´t understand is the huge difference.