You know Activision made bad decisions on who they used to port the game. That was their biggest mistake, or they just didn't have the two teams collaborating together/on the same page.
The truth is though, Activision could have ignored this entire mono problem. Most people wouldn't have cared or even known there was a problem. But, you have to them props for spending the money to correct the problem...and it gives them a chance to correct other problems.
They know Wii owners still want to be able to download songs for GH3. Why not work on allowing extra content to be read of the SD card directly, allowing for a Gig of extra memory for songs. It should be easy to do. Or how about putting that 2 Player Quick Play option back into the game?
And when you say Activision won't spend the time to do this extra steps? Why not. It will cost more to implement, but also provides the opportunity for making more money with download purchases. It just may mean they will recoup all their loses for the replacements.