I am running 4.8.3 now. My system was up-to-date and all attempts to run the update failed and the initial look at the repo failed to find the kde4 list in the repo. It wasn't until I changed kde4 to kde that everything worked again. Your information is very confusing and I don't see it as valid because it does cause confusion. The natural thing is for people to update. They can't update unless they change the repo section list from kde4 to kde.
For those of you who want to update change your kde4 in the section list where you set your repo target to kde and your system will be able to update. If you don't every time you open synaptic and click on reload you will get errors and will not be able to install or update anything.
By the way my system is also updated but is running KDE4.6.x
It failed because you are using KDE4.8.3 which requires the section KDE. If you were still running KDE 4.6.xx it would use the section KDE4
Some people are not in any hurry to upgrade to KDE4.8
I for one have problems with it on several different machines.
Again it only fails if one has changed to KDE 4.8.3 If they have made the upgrade to KDE4.8.4 than they need to be using the KDE section in synaptic