There is still code in Civ4 that turns overflow in gold payouts. It just almost never returns overflow gold > 0. There are weird theoretical late game situations where you can still gain gold from overflow. The funny thing about those is that get overflow twice one the full overflow in hammers (hammers not above the overflow threshold) and part of it as gold payout on top of that. So the evaluation of the BUG team that Firaxis goofed up is almost certainly correct.