Back when Shimano first came out with 10 speed they produced a "10 speed only" freehub. I believe this lasted for 2 years and was then discontinued in favor of the more acceptable/better current version on the Shimano splined freehub body. You may need to have a rear derailleur adjustment when you go to the new wheel - or you may not. If you do need a adjustment -- most likely it will be minor.