Ok. Let's try this again. Please let this thread die off. The question posted was answered and there is enough bad blood here already. Please don't add to it, I don't want to see another thread get locked due to poor behaviour.
Sorry Ishar, I just wanted to try to scientifically answer some of the questions based on what I've learned about coldwater fish, like goldfish, being kept in tropical environments.
In regards to the idea that internal organs continue to grow while external don't, I haven't found much conclusive evidence for this. As a scientist, I'd like to conduct my own experiments, but I don't do this particular one for ethical (my own ethical beliefs) purposes. There may be some truth to this, but their internal organs wouldn't continue to grow until they popped. Their bodies can only accomodate a certain amount of growth before it kills them. What I gather most from a fish being a space too small for it, is that its growth will be stunted, certain internal organs will not grow to full size, which will drastically lower the life expectancy of the fish because their organs haven't matured enough to do their required functions.
In regards to different temperature requirements; As a geology student, I'm a very firm believer in Darwin's theory of evolution. If a species is to continue to survive, it will have to adapt to new changes, or it'll face extinction. I'm sure that goldfish have began to adapt to wider temperature ranges, since they aren't an endangered species. Like Brian said, they're surviving and thriving in areas where the bodies of water reach tropical temperatures.
The biggest problem I'd see with keeping a goldfish in tropical waters is that, as coldwater fish, their metabolism will react differently. At certain temperatures, they won't be able to digest food very well, and certain foods they'll metabolize more quickly, requiring them to eat more, and produce more wastes even quicker.
Hmm, maybe the scientist in me will want to conduct a long-term experiment after all...
Here is what I'm proposing in doing after the summer is over and I get back home.
Instead of making my 20g cherry shrimp tank another very lush planted tank... I'm going to do an experiment with a goldfish.
I'm going to keep a solitary goldfish in my 20g tank, in tropical conditions, for its entire life, however long it may be. I'll try to keep a journal that's updated at the very least every week, showing the progress of the fish.
I'll map out a whole thing, and make it all scientific later on... I've got to get back to studying for finals!
Edit: Agh, sorry Lotus, I was typing all of this as while you posted what you did.
. To be honest I'd keep a close eye on them. While it *is* possible they are simply "hanging out" together it is also possible that may be an *extremely* mild form of aggression (ie: not enough to worry about as is) and *could* escelate. No, if I could actually *see* the fish interacting I could say with more certenty but that's probably not an option lol 
