Yes...the 80 hours ONLY involves the time you spend with direct patient care. Therefore, if a program wants to they can have you charting until the wee hours of the morning. Or slaving away in the books somehow.
However, I haven't heard of many anesthesia programs who do this back-handed kinda thing. But if you're interviewing, it would be wise to ask the residents what their REAL hours are. When do they actually go home.