I guess what I'm asking is what rules, if any, prevent that (absurd) example from being actually illegal?
I'm sorry, but answering that question would constitue legal advice, and IANAL. -Rob
The sticker on the back doesn't tell you how much it uses in practice, it tells you the maximum it will ever use. It's useful for sizing circuits and picking fuses, but not for estimating running costs. The label on the back doesn't tell you if it uses 80W or 1W in standby. It doesn't tell you if the maximum rating applies during normal viewing, or only for two seconds at startup.
To find out how much power something is using you really need a "Kill-A-Watt" meter. Google it. They are quite handy! -Rob