Well actually libogc provides SDHC card support regardless of the IOS, see this great article by sven: http://www.dcemu.co.uk/vbulletin/threads/170430-SDHC-support-for-the-WiiLego Batman uses IOS33. That IOS doesn't support SDHC. Bannerbomb runs under the System Menu IOS so for newer System Menus SDHC will work, but I guess it won't for very old ones...
It means that LEGO games only support SD cards because Nintendo dev kit for PPC didn't support SDHC cards at that time.
That's why in my previous post I didn't mention IOS (remember that a IOS runs on ARM).