There are two elements to remember:
- It takes a year for the magic might being to start counting as a tether. During that period of time, they are vulnerable to acclimation;
- The tether is normally Magic Might / 10, and the rule to prevent acclimation requires a magical being to always be within an aura of strenght = Magic Might / 5. Incidentally, this means that magical beings generating tethers will normally settle in a magical aura anyway - because the tether isn't enough on its own to shield the creature generating the tether from acclimation, unless A) the tether adds to other tethers in an existing magical auras to the degree the aura becomes powerful enough to protect the new resident ; or B) there are more than one such creatures in an area and they collectively increase the prenatural tether score enough.
As for the implication, I believe what is implied is not so much in regards to implying an immunity to acclimation, and it's just a simple statement that magical beings generating tethers need to find an aura since they can't generate one. The primary rule regarding acclimation is in a separate chapter, and makes no mention of tether-generation.
Acclimation is aging for magical creatures... if you do not allow immunity to aging or warping as a virtue, you probably shouldn't allow immunity to acclimation either. There's a reason Elementals, animals of virtues and dragons don't typically settle down in a dominion-dominated urban environment - they will fade away. If they could simply shield themself from acclimation by their very presence, Mythic Europe would start to ressemble a more typical fantasy world, and the magic side of the setting wouldn't be as mythical as it is, because it could easily be in your face anywhere.