Booth's circumstances seem to be the perfect combination low mpg extreme, the high mpg extreme would be someone on a 30 mile commute who does a constant 60mph all the way there on clear roads. On my way to work, my 33mpg commute for 20 miles takes 25-30 mins and falls towards the best you'll see as the roads are pretty quiet. On the way home it gets a lot busier and it's a 45-50 min commute, but the mpg doesn't drop hugely - 31mpg.
Because there are extremes (you and I possibly towards opposing ends of the spectrum), IMO far more sensible to state an average mpg somewhere between the two, to anyone considering an R and looking at the numbers. Better and more realistic than giving a worse or best case scenario as being the norm.
