Discarding offline bidders for the moment. If one person has 10,020,145 zeny on them, and another person bids 10mil. They can't outbid due to the fact that they can't add the bid increment onto the starting bid, totaling 10.1mil. Since your offline bid was 10mil and the bid of 10mil was taken by someone else, the GMs couldn't go higher for you.
EDIT: The GM service offline bidder incident isn't an equal bid one. It's that the offline bidder had bid -more- than the in-game bidder won it for and therefore would have raised the bid, but the GMs forgot about it.