The Swiss haven't annulled visas for my acquaintances in much the same circumstances; and so the claim about what could happen to the visas seems to be speculation on the part of LH.

LH and even German Foreign Ministry reps are not spokespersons for the Swiss government in such situations -- thanks to Germany being defeated in WWII -- but it seems like they are making representations to that end anyway. LH may have been concerned about avoiding a fine or repatriation costs were the passengers to be denied entry but that doesn't mean their assessment of what probably would (not) result is beyond reproach.