Mark,
Thermos can SURVIVE higher temps, Mesos generally cannot. So if you do a blend and then cook to higher temps, the Mesos will die mostly off. In this style of make, the Mesos are important for early acidification, then the Thermos take over as the dominant culture.
Consider this. When you make a true thermo cheese, like a Parmesan, the curds (and bacteria) are only at higher temperatures for a relatively short time during cooking. After draining, the curds cool quickly, and obviously reach room temperature during overnight pressing. They are cooled down even further at cave temps during aging. The thermo bacteria remain active and continue to do their thing long afterwards. Even after the lactose runs out and the bacteria die, they bring a whole different set of proteolytic enzymes into play for long term aging, flavor, and texture.