Actually, if OS X.6 is so close to X.5 then most users will likely not care to update. This would also function as a way to give programmers (MS, Adobe, Accordance-which is more important to me) a cushion period during which they will have to take seriously the need to move to a cocoa framework. From a business perspective, it is win-win. Force developers to change and don't make consumers feel like they are missing anything if they can't/won't update.
Oh, Apple also wins because they will still sell the new OS but I think they are more concerned with positioning the future direction of OS X than with sales with 10.6. Their money is made more with hardware than software anyways - think how Apple sells music and movies at a loss in order to sell hardware with a better profit margin.