Even if the Wii can only handle 2gb cards, wouldn't that be enough for most people? Heck, the 512mb of internal space is probably enough for 75% of Wii owners out there, and a 2gb SD card would add 4 times as much space as the Wii already has. That would be enough for a LOT of VC games and saves, but even with that there'd still be some hardcore Wii owners who would need more, but if that's the case they can still swap cards about.
The Wii doesn't need as much space as the 360 or PS3 does with their HD content and so forth. The competition might need 200gb of storage space, but would that much space ever really be used by the Wii?