Not quite accurate mrmrssmith, i often book tickets to USA within 72 hours of departure, sometimes even on day of travel and have no problem with providing this info within hours of departure.
Correct. The limit for getting ESTA authorisation is essentially close of check in. The 72 hour pre departure recommendation refers to the fact it can take up to 72 hours to receive the ESTA authorisation. When ESTA was brought in in January, there were many cases of people not knowing about the requirement, turning up at check in, the airline knowing they don't have the authorisation, and sending the pax to the nearby internet cafe to obtain it. And I'm sure there's still a few cases each day...