The two-man development team is having trouble compressing the game under the WiiWare limit.
http://www.nintendoworldreport.com/news/24381
Super Meat Boy developer Team Meat announced via Twitter that their game isn't coming to WiiWare in November like originally planned due to the fact that it is currently too big for Nintendo's download service.
The tweet read: "attention internets, the wii version is NOT coming out in Nov its impossible. we havent even gotten the size down under 50mb yet (goal=39mb)"
The Xbox Live Arcade version came out last week and has been getting rave reviews. The file size for that version is around 90MB. The WiiWare file size limit is around 40MB.
The XBLA version also features an exclusive world, called Teh Internets, where new levels will be added by the game's creators. The PC version is still supposed to come out soon.