That is correct, but...... a tank in the lower range has some benefits. If you can keep your tank at 72, you will have slightly decreased algae growth, and more importantly you may have less issues with disease. The spectre in any seahorse tank is the threat of bacterial pathogens like Vibriosis..... this is a catch all term for diseases caused by the bacteria in the genus Vibrio. Many ulcerative diseases can trace their causes to Vibrio bacteria, such as snout rot, tail rot, and other skin lesions. Vibrio is pretty common in any tank (in fact, like many bacteria, it's just plain pretty common anywhere...) and is usually only an issue when (1) the animal is stressed due to poor water quality, or (2) something causes a bloom in the bacteria population, which can potentially overwhelm your seahorse's immune response. Keeping the tank at a lower temperature slows the division process of the free bacteria, thus keeping the general population of these little buggers at a low count.
There are drawbacks to the lower temperatures, of course. Most of our tropical corals will not grow quickly in these cooler temperatures, for instance. Many seem fine, but may not be as....prolific....as you will see in a tropically maintained aquarium. In my very humble opinion, this is a minor price to pay to help keep our seahorse critters healthy. If you could maintain a constant temp of 72-74, you should be fine.