When I clicked through, the hardcover edition was priced at $13.98 while the Kindle edition was a dollar less ($12.99). I think that Amazon's prices change pretty frequently, which might explain why you saw a different price at the time you checked.
Hardcover: 13.98, Kindle: 14.58
The price is the same during the past few days, I just wonder if Amazon display different price to different users based on their location.