You are absolutely NOT the only one who is disappointed. I emailed P&R about it before the book was released, as it had been advertised on their website and a number of other booksellers' website as going to be available in a paperback edition. I never received a response from P&R. Therefore, I looked up Hoffecker's (the author) email address and asked him about it. He sent me a very kind and prompt response indicating that it was the publisher's decision due to the slow sales of the other books in the series. I still wonder why the first book in the series was on John Williamson Nevin. Why not Warfield or one of the Alexanders or Thornwell, etc.? They seem to me to be larger figures on the American Reformed landscape than Nevin.
I wish P&R would've possibly limited the number in the print run or done whatever they would've had to do to publish this in a uniform manner as the others in the series (i.e., in a hardcover edition). In addition, in my opinion they gave the greatest figure in the series (Charles Hodge) the worst binding in the series (paperback [though it is bound in a quality paperback edition]). Maybe Chris Coldwell or Don Kistler (or any others) can weigh in on this and shed more light...
Grace,
Van L.