Nintendo has enforced a size limit of 40MB for any original game that is to appear on the Wii Ware (known here as Wii Software) download service.
This, in case you don't know, is a very small amount of space for a whole game. Storage space is an issue with Wii, and although Nintendo insists Wii doesn't have a storage problem, these are clearly measures taken to stop Wii Ware games from clogging up the system.
Another of Nintendo's restrictions is to the number of releases any one company can make on the service - no more than one a month, which is reasonable. If companies are banging out games that quickly they'd probably be not worth the their disc space.
And, according to IGN, most of the games are being made on a budget of under $100,000 which, in this day and age, is nothing.