Squishyfish, I don't think you are arguing. Don't worry.
But I don't think my point is coming across. Let me try again.
What temp do you keep your home at during the winter months? 68 deg? 70 deg? Let's say 72 degrees, as that was mentioned before...
As an example, I found a site that lists the average ocean temperatures in Fiji throughout the year. It ranges from 77-82 degrees throughout the year. So I would assume based on this that is the range these fish, corals, etc., typically thrive between.
So if your tank stays at 72 degrees because you keep your home at 72, that is still 5-10 degrees colder than these fish typically live in.
I don't think the topic of home temp versus outside temp versus tank temp has anything to do with this. The simple fact is that if you do not heat your tank, and your home stays at 72, your tank is colder than what the optimal temp should be for your fish.
If your home is heated, the only thing the outside temp should affect is how often your heater comes on, and how long it is on for. But I don't understand how that comes in to play in the question of "there is no heater in the ocean, do you need one in your system?"