I don't think what you are expecting or encouraging is a bad idea, the use of SD cards, however I do find it more likely both the handheld and console will be optical, based on some sort of disks (many mini again like the Gamecube?) and that (similar to a PC as you mention) the main console version will play the games at an extremely higher quality than the handheld but the games will be more or less the same
obviously they are mostly likely aiming to integrate the 2 systems with the same software. the fusion integration idea is fantastic for Nintendo to do because thy obviously have a pull on the handheld market and if someone purchases a handheld and then realizes they can play the same game on the TV with better graphics they might feel compelled to buy the console as well if they otherwise wouldn't
I'm not familiar with SD cards in depth but I do wonder whether or not they are efficient at holding enough information
