Actually, miles travelled is a stat that skews in favor of the long distance side (longer trips are given more weight). If you count trips by frequency, long trips are even less common.
I decided to dig up the source again (I was going by memory). In terms of miles, according to the 2009 US National Household Travel Survey, 357,366.43 million out of 2,245,111.45 million miles (15.9%) are on trips over 100 miles.
In terms trips, 1,658.09 million out of 233,849.36 million trips (0.7%) are on trips over 100 miles.
NHTS Data Extraction Tool
I use the miles figure because that is what is relevant for Tesla in terms of determining how many lifetime supercharger miles they can expect per car.