If they release this as regular DLC for the Wii, there will be outrage from the (far larger) PS3 and XBox gamers. "I have to pay $15 when all I want is 'Metal Health'? But Wii can just buy that one song for $2. WTH!? I hate Harmonix."
If they release this as a pack-only item, what do they charge? $15? Then they get moaning about, "Why do I have to pay the same price when I don't get the Blitz game! It should be like $10 for the Wii. The Wii gets screwed again. WTH?! I hate Harmonix." Fine. They charge $10. All the XBox and PS3 folks go, "I don't want that stupid Blitz game. Why can't I just get the songs for $10, like the Wii? WTH! I hate Harmonix." Do they charge $20? Then they get moaning about, "Why do I have to pay more when I don't get the Blitz game! It should be $15, like the other consoles. The Wii gets screwed again. WTH?! I hate Harmonix."
I think Harmonix will make an effort to get these songs on the Wii, but there are a lot of landmines that they will need to step around to not have this blow up in their face.