That means absolutely NOTHING for the user. As soon as the software is installed, it will work that way regardless of what MS wants to support it or not. I've installed it anyway long ago, but I don't really care about the support, Windows will work the very same way.
Oh! There IS a legitimate reason to NOT install services packs! In my work machine, as soon as I reboot to install SP1, it just crashes for half an hour, then reverts the changes and report some incomprehensible error, so it just don't works. The same with EVERY update. So I gave up, run on RTM forever and without any updates, I can live without them, and Windows seems it can too.