Léonie,
Thanks. That makes sense of why I could find no software update to download.
You asked:
"Is there a reason, why you want to stay with Mac OS X 10.8.5?"
There is one particular open source program (Hugin) that is essential to my work-flow and I was waiting to be sure that it was compatible with Mavericks. Others have confirmed that it works fine. So I will move to Mavericks when I have a spare evening.
In general I am cautious by nature ... I usually let the keen brave people install the latest everything. Then when any incompatibilities have been ironed out I update to 10.x.1 knowing that my essential applications will work.
Thanks