Are 'Thank you' emails expected at every level?

I understand sending them when you're a college student interviewing for a job. I also understand them when you've been in the industry a couple of year and are interviewing for that next step up, be it a Senior position or even a Manager level. It's more of a formality than anything else, and really just common courtesy.

But does it stop at some point? Do you send Thank You emails to VPs when you're interviewing for a Director position? Or Senior VPs when you're interviewing for a VP? I'm just curious if they are just as common at this level.