Perhaps he likes a REALLY upright position. Unless he has the seatpost waving up in the wind though, I have to imagine that it's murder on his knees if he goes any significant distance.
For what it's worth, I'm 5'6", and I prefer my touring bike to have a 52cm top tube. I find it's just about perfect for my relatively relaxed posture. My "go-faster" bike, OTOH, is 50cm, and it's perfect for the riding I do on that as well - a lot of it has to do with the particular geometry of the bike in question.
__________________
Knows the weight of my bike to the nearest 10 pounds.