The person you sold the Wii to though would still have access to the games, right?
Not if the Wii was formatted before selling, which is probably a good idea.
But just disconnecting the console from your Club Nintendo account (without formatting) does nothing of value. Any downloaded games will still be on the console. Any download history you have is still tied to the console. The only difference after removing your Club Nintendo information is that you would no longer get credit when new digital downloads are purchased; existing records don't matter.
Could somebody please next time they talk to Reggie or any Nintendo Representative ask them about people that have VC game purchases and Wii Ware titles associated with their Nintendo.com account, but not connected to a Wii, because they sold their Wii...if they can transfer or get those games back. This is the KEY decision on whether or not I buy a Wii U...and I hope Nintendo delivers with a yes...because right now, I have $100s of dollars of virtual games nobody can play...and are easily recognizable as my games on my account and not attached to any system yet.
Lots of sympathy... but I don't see how anyone could reasonably expect this to happen.
How can Nintendo or anyone else know the games aren't still attached to your old system right now? There is no way to check, no activation/deactivation process for Wii, and no meaningful tie between your Club Nintendo account and the hardware you are using. The console simply wasn't designed with that type of functionality in mind.
Hopefully what you suggest will happen in the future, and Nintendo will allow users to link purchases with an account system that can then be activated/deactivated for specific hardware as desired. But that type of system isn't in play yet and certainly wasn't around when you sold your Wii.
My guess is that you'll just have to live with the consequences of your decision. Tying downloads to hardware was a bad decision, but the rules were pretty clear and generally well known. Maybe you didn't understand how things worked, maybe you didn't bother to try and educate yourself before making an irreversible decision, but it's too late now.
(Also, stolen Wii consoles are given different treatment than sold consoles. More than one person has been able to retrieve their downloadable games, with some effort, in this circumstance. This has been discussed in the forums and on recent podcasts more than once. Having a console stolen isn't the same as choosing to sell your system though.)