I found this slide amusing from a presentation called Making the Switch: Unlocking the Mystery of the WISC-IV by Shelley C. Heaton, Ph.D.
http://www.phhp.ufl.edu/~jhj/WISCIV.ppt#2
Why another revision?
A. Keep us on our toes
B. Revisions to theoretical foundations
C. Make more money
D. The old pictures were ugly
E. Improve psychometric properties
Answer: B & E