I have reported this problem to App World Vendor Support and they inform that they have their internal people investigating the issue and will get back to me as soon as we have an update.
As soon as I know anything, I will post it in the thread that I started last Saturday
App World Issue - update option not offered for new version
In the meantime, if anyone knows of a sure-fire way of working around the issue (that does not involve deleting the app) I would sure like to know about. Some people have had luck searching for the app in App World or refreshing the installed list in My World, but results are mixed at best.