The design of the shop on the Wii is largely to blame for this. Or maybe even - the deliberate CHOICE to design it that way.
They chose to treat every console as a seperate account - you could begin buying games on the shop without having actually linked the console to a MyNintendo / Club Nintendo / Nintendo VIP account. In theory - thats a good idea. People don't have to be regular members of the Nintendo community before they can give Nintendo money.
The downside is the implementation. There's no persistent exchange of information between the console and Nintendo - maybe for privacy reasons, who knows - but Nintendo have no walled-garden so to speak, no user-account system they can monitor and ban people from. The record of games you own is actually held on THE CONSOLE and not on the server side. This may have changed now because this was a long time ago, but people who had pirated VC/Wii-Ware games actually found that if they went into the Shop - they were able to legitimately REDOWNLOAD titles they hadn't even bought. Even though Nintendo OBVIOUSLY held the purchase information and had an audit trail - the shop channel wasn't actually checking to see if the console in question had a license to use the software properly.
So whats needed is:
* Nintendo need to go back through their books, write a program to go back through the system, or just employ someone to link purchases to console IDs
* They can then do a Wii Update with a new EULA / TOS and state that if people have an account linked to the shop, that they are linking all prior purchases to that account. As a result of the above actions, downloads would be transferred from System accounts to User accounts.
* THEN and only then would they be able to make them transferrable
* It may even provide them an opportunity to prosecute pirates if they have the shop report back any red-flags