re: Are 'Thank you' emails expected at every level?

It probably depends on the company you're interviewing with and the industry you're in.

I work in ERP (accounting and IT) and for new hires we make the hire/no-hire decision within half an hour of the last interview. So a thank-you note is basically a waste of time for everyone. For senior hires it's a little different b/c usually you know someone going in.

Other businesses may be different.