I don't know, but you get the extra limitation of USB2 being half duplex. USB2 is something like 480mbps. Add half duplex limitations and just general overhead compared to theoretical max. I can see how some network protocols become limited to 60mbps.
True. It does depend what else you are doing with the pi. Something like a USB hard drive could account for that poor performance, especially if you were upload from/downloading to it.