I know putting a microSD card higher than 32GB into a Nintendo 3DS only works if it is formatted to FAT32, and so Nintendo just says the cap is 32GB to avoid confusion.
"Nintendo cannot add support for SDXC cards because they come formatted with with exFAT, a Microsoft proprietary file system for which Microsoft holds a patent. When the patent expires, Nintendo could add support for SDXC cards formatted with exFAT.
Until then, like you said, if you buy an SDXC card and format it with the FAT32 filesystem, it should work on the 3DS. In theory, the capacity supported could be as high as 2TB (the upper limit of the SDXC standard as well as FAT32)."
Don't know about any other devices, though I would imagine the reason is similar.