Time was that the Dolphins had a bit of a home field advantage in September and October. Heat undoubtedly played a part in that. Sure every team opens camp during the summer, but the heat and humidity in south Florida is really something. Practicing in those conditions helped the team to prepare for it in the first few weeks of the season (and sometimes later).
But, we're seeing a levelling happening here. Players are overall in better condition that they used to be, even early in the season. And there are measures in place to counter the heat. At the Orange Bowl, and in the early days of Joe Robbie Stadium, fans were the only relief players had, and having the visitors on the north side of the stadium placed them in more direct sunlight.
Now, they have these relatively low-tech (by today's standards) cooling systems that players can wear under their uniforms, which basically hook up to a portable air conditioner, to lower the player's temperature. And I couldn't help but notice that the Jets had a couple of people assigned to the task of holding an "awning" (really, a long strip of UV protection screen material) over the players bench, which provided shade, and probably lowered the temperature at the bench by 20 degrees.
Its no wonder the Jets had no trouble with the heat. And its unlikely any other team will, either.