Miles are irrelevant, the statistic could get you on your first or last journey.
No, miles are the only reasonable statistic. I see what you are saying but people dont make random pointless journeys by air, there is a purpose. Any similar journey is safer by air than by road by a large factor depending on the distance. Comparing journey for journey is as relevent as saying that as a human being i am at least 1500 times more likely to die in a road accident this year than an aircraft accident taking no account of exposure to either.