First of all goldfish are not coldwater fish, they are eurythermal meaning they can thrive in a very wide temp range. They are native to the tropics as well as subtropical areas. They are naturalized in almost every body of water all of our other tropical fish come from.
Second most of the time the temp difference between room temp (goldfish) and tropical is 4-6 degrees F, not a big difference for many fish.
Third, there are many fish that are considered tropical that are actually from cooler waters. All of the following are fine at room temp: platy, guppy, molly, swordtail, zebra danio and all variants (leopard, blue, gold, glofish, longfin varieties of all of these), white clouds (normal, gold, and longfins), bristlenose pleco, Siamese algae eater, and many more.
For accurate information on actual wild temp for a species you should check fishbase.org. It is used and maintained by scientists so it is a lot more accurate than the hobbyist sites that just regurgitate what the last hobbyist site said.