A "sync only this topic" wouldn't work where you have new links appearing in the topic that are related to topics that you aren't yet synced. The links are created locally on your PC before being uploaded to the server, so these would become broken links in the player's copy.
There are (most likely) other dependencies that are affected in a similar manner.
Valid point - and don't we hate those?
I do not know how the code behind the program works, but this is what I would like to have. Maybe the wizards at LW can figure something out.
As for links - depending on how the database is organized - I might be lucky and the links (in other topics) could be updated simply and easily along with the topic I want to update - without updating all of the links.
Ah, well - we place our more or less insane visions and wishes in the fora and LW probably swear silently while trying to see if they can be implemented.