Probably just money, I know someone that put the 07 struts on a 06 K9 for that very same reason and everything lined right up. You could always sell the old ones on ebay to recoop some of the cash.
Cavracr21 did the swap along with his dad's K9 as well. Its a direct replacement shouldn't be hard at all. Do a search on this forum and you'll plenty of strut replacement posts.