Apparently, there's another major restriction relating to DLC on Wii for music games - no bundles. Rock Band 2 will not feature any of the bundle savings as Nintendo "does not allow duplicate content on the music store." So it was a choice: having the ability to choose individual songs, or the savings of bundles. They chose the former. GH:WT apparently has the same restriction.

But one would think that a bundle might show up if it was impossible to buy the songs separately anyway, correct? Apparently, because of the "memory buffer" thing GH:WT does to use DLC (you have to keep 200 blocks free on your Wii's built-in memory for the game to use as swap space), a bundle would be technically impossible as it won't fit. And since the new Jimi Hendrix pack for GH:WT is bundle-only because of some Hendrix estate-related restriction, that means no Hendrix for Wii owners. Which, well, sucks.