I have not seen Punch Out shortages, however EA Active is heavily marketed in stores and in non traditional VG TV (Survivor, Biggest Loser Finale, Ellen all had ads or features), while most Punch Out ads I've seen have been on the web, or G4.
I think it will just be more popular 1st week and lifetime than Punch Out. Wii Fit really opened up a door to a totally different customer, as all fitness games on the Wii are selling (MyFitnessCoach, Gold's Gym, Jillian Michaels, etc). And EA Active is the only game actually marketed since Wii Fit, and they used the same template (in store flyers, DVD's, talk show circuit), and added celebrity endorsements (Bob Green, Alison Sweeney). There's no way it won't be huge, and it will sell consistently instead of relying on legs.
Punch Out will be huge, but will be a "legs" title, Boom Blox will outsell the first and it will all be legs.
Wii Code 3456 7941 4060 2924
