Many of the facilities that will allow seasonal drops down low are showcasing animals found in regions that also have that temp swing. As an example, South FL water temps will dip down into the upper 60s for a short period in the winter. The marine life will drastically slow down, but survive. (Side note: surviving and thriving are two very different things.) If it lasts too long, mortality spikes on the reefs here. A few years ago, we had record cold spell and it wiped out a very high percent of the coastal fish and inverts.
I've been in the public aquarium industry for about 15 years. Not all do it this way. In fact, very few do it this way. despite what anyone says, it's not a great idea long term. There are short term benefits (slower metabolism etc...). Most places run water for tropical marine fish between 75-80. Displays specifically for cold water species are maintained at lower levels that will match the area the fish are found.
I wasn't advocating it nor knocking it. I was simply stating I've witnessed it, and did not see any signs of stress on the animals. In fact, their corals displays looked very good with bright coloration, good polyp extension, lots of new growth etc.. They also kept a FO display with huge versions of angels, tangs, triggers, moorish idols, groupers and more, all at right around 70.
Personally, I strive to keep my aquariums around 78 degrees, and find that to be where I have the greatest success. Certain fish that are common in the trade, especially ones with large distributions like gold rim tangs, moorish idols, various wrasses and groupers, I wouldn't think twice about keeping them at lower temps. A lot of these fish's distribution extends all the way to the Eastern Pacific, where they are subject to a lot cooler temperatures due to the up dwelling antartica currents.
Personally I think rapid temperature drops are much more devastating than low temps themselves. If temps are gradually lowered, many animals seem to tolerate temps not normally associated with tropical aquariums. One example of this, from personal experience, are cichlids.
I keep various old and new world cichlids. In the summer, I keep many of them in an outdoor pond that ramps up and down throughout the season. I realize cichlids and marine fish are apples and oranges essentially, but these fish survive and seem to thrive at temps outside what is recommended.