Which I may be wrong... It is the formatting of the card that the device cannot read, not the extra data. They changed the formatting to handle the larger data, and the ability to read and write faster. The cards changed formatting FAT16 (SD cards 2GB or less) to FAT32 (SDHC 2GB to 32GB) to (exFAT 32GB to 2TB) A couple companies found a nich where they can format a 4GB card with the old FAT16 format and still be able to have all the data read by the device.
Windows on the other hand still thinks a 4GB card must have the newer format.
From what I found the cards are at least twice as expensive as regular 4GB cards and harder to find.
A plus for the people running older stuff that wants a higher capacity.