How many US airman's certificates are revoked, roughly, per year?
FAA Order 2150.3B, Appendix B lists violations and the civil penalties (fines) and certificate actions which are to be imposed by the FAA. The rest of the document also discusses how investigations of certain violations are undertaken and thresholds. That order gives much more detail than you'd ever want to know.

A common theme is revocation is called for when the action is intentional.

These are what are the FAA initially charges you with, so they are higher than what actually happens. A certificate action is either negotiated as a settlement, or if it can't, it goes before an administrative law judge, then appealed to the NTSB, then appealed to the Federal court system.