I have a n800, with the latest firmware and a 16gb card, and it works fine without any issues. (except for the memory corruption issue, which seems to happen every few months, regardless of the size of the cards, as it happens to my 4gb and 8gb cards as well).

So I'm guessing that the 8gb in their literature is either because an earlier firmware didn't support any higher, or because at the time of writing (many years ago) they didnt yet have any larger cards on the market.