Except that the last data point received is still valid as the aircraft's current location, even if it came in several hours ago - which we may well care about. That is, some users may need to see where a given aircraft (or the entire fleet) is, even if an aircraft hasn't updated in a while. That said, I did discuss this with my higher-ups, and got the ok to take it down to four hours.
Note that in your explain output nothing is filtering by time at all; are you sure you posted the right explain?
I thought that as well, but then I noticed that the depesz site truncates the data in the html view. Switch to the text view and the filter is there, as part of the index condition, after the long ANY list. http://explain.depesz.com/s/H5w