Btw. Things seem always a bit faster after an incremental upgrade:
1) The system is optimised while installing.
2) There certainly ARE improvements, albeit small ones.
Usually, the 10.x.x upgrades are small upgrades that update individual packages, like CD-RW support and graphics card support and the like. For some, those are very, very important updates, because their hardware wasn't supported earlier, or supported only half-heartedly.
However, the latest updates have been quite big, and I still don't quite know what exactly made them that big...