No where in the study did it mention the capacity of the players; its more likely that, due to their relatively low cost, there were a higher percentage of small capacity players then high capacity ones. Thus there will be an artificial low average of songs if you physically can't carry that many around with you. People will carry more music if they have more space a survey from 2 years ago is less relevant due to the capacities we have now.
I would have liked to see more specific results, like what the average on high capacity machines were. 0-5GB, 5-15GB, 15GB+.
I do know, from my own history, that if I have larger capacity I will carry more music around with me. I had cap at 4GB, which is only 550 songs, so I would have room for videos. If I had larger capacity I would carry more music around with me. I doubt I'm in the minority here.