I had never heard of constructive dismissal before so I looked it up in wikipedia: http://en.wikipedia.org/wiki/Constructive_dismissal. It sounds like employers in Australasia and the U.K. have much stricter policies on conduct. I would guess that a significant percentage of (North) Americans would feel justified in resigning their positions based on these actions by the employer:

• Putting managers into excessively difficult work situations without supporting their decisions.
• Harassment or humiliation, particularly in front of less senior staff.
• Sabotage of employee's work product either directly or indirectly with repeated interruption, confusing or inaccurate direction, or uncommunicated deadline changes.

Many U.S. states operate on the "employment at will" principle, meaning that either the employer or employee can end employment at will, unless governed by a written contract, which would be unusual except for a union member or key executive.