No, it is not even close to normal for a belt to wear out at 18k miles. And this comment ("this is not unusual with this model due to the engine power output") is pure BS. If they think a CVO110 is some sort of fire breathing, belt and tire shredding high performance monster, they obviously lead a sheltered life and probably ride a moped as personal transportation. Just sayin'.
Belts can fail for all kinds of reasons, from just getting a bad one from the supplier to damage from rocks and debris or even high levels of ozone. But the majority, even on the fire breathing CVO models, last 50k or more miles unless they are damaged somewhere along the way. If you have those folks replace yours, I'd tell them I want the old one for my review. And if there is damage, they need to closely inspect the pulleys. Putting a new belt on damaged or severely worn pulleys will result in doing this all over again fairly soon.
Jerry