If a patient has anything in their stomach, water food etc when the anesthesia provider goes to intubate, the patient may aspirate. I've seen it happen, and the outcome for the patient isn't good. The rules for clear liquids are slightly different but I know many anesthesiologists that are stringent with these rules. I think they should be...it may seem like overkill, but better safe than sorry.
In my hospital, if you have something to eat or drink before your surgery when you're not supposed to, surgery is canceled. Unless, of course, it's a dire emergency or trauma.
And obviously, we CAN'T trust patients or nurses to follow the guidelines...plenty of patients are still getting fed when they're not supposed to.
I would think "nothing to eat or drink after midnight" is pretty dang straightfoward, but apparently not.