As far as I understood this, the GPSmap 278 can address 2GiB. This happenes usually when the firmware only understands FAT16 formatted cards. FAT16 is limited to 2GiB, but usual 2GB cards have only 1.86GiB as Ballebar pointed out. So there is a gap.

I think the trick with the russian card is, they use a 4GB card and partition it to a 2GiB first partition and an unused rest space and format the the 2GiB partition with FAT16. So you get a FAT16 formatted card with maximum space. This could be done in principle with any harddisk partition manager, although storage cards sometimes behave a little bit different compared to harddisks, and I don't know whether the GPSmap 278 understands all the possible partition tables correctly. SO it might be necessary to fiddle around a little bit.