I fully agree with your opinion about the first incident, the nodule. If you force your instrument to sing outside its comfort zone ("on your capital"), and you do it often (of course nothing should happen if you just sung the odd evening something not appropriate), likely there are problems waiting for you in the near, or not-so-near, future.
But Ms. Dessay was not reallly happy with the repertoire of a light lyric coloratura voice, and she tried heavier roles, even if she was fantastic on her natural grounds.
This happen all the time, to many singers. Now, and in the past. It's just the nature of the beast.