I found a strange behaviour when at some blogs did, manageed to get the auto-update for wordpress to work, without any effort, but for others need to use the ftp transfer.
What the problem was, that the Apache user/group was not able to update by using the standard WordPress plugin, found in the plugins directory.
The group rights was not the same group as Apache was using. By changing the group owner, of the wordpress directory (did it recursively) I was able to perform a automatically update.
sudo chown 775 wordpress