I don't think I understand how invulnerability could work for the ears. Don't the ears pick up vibrations to hear? If they were too dense, then "invulnerable" characters that do no have super-hearing like Hercules and Hulk* would surely be deaf.
On the other hand, invulnerable charactes like "Superman" who do have super-hearing while perhaps not being deaf, would still vulnerable since their powers compensate.
Don't even get me started on Daredevil and Wolverine. If you wanted to beat those guys, just use a whistle to mess them up.
* Unless it's now the angrier he gets the better his hearing also becomes.
We've seen super-hearing turned into a liability.