Well guys, you are right. It doesn't make sense, and it will never EVER be real either. The 737 is almost already overpowered with it's CFM56 engines, so there's no meaning or reason at all to add a tail engine.
The picture was edited in photoshop by me. I took the tail engine of a Lockheed L1011 TriStar and mounted it on the 737 fin. And I'm happy you bought my little "scam" ;D
here's the original picture
http://www.airliners.net/open.file/352629/M/Pretty nifty crafting from my part, eh? ;)