The max theoretical speed is the same, but the max actual speed can vary. People are usually interested in the actual speed. Or they should be: if you're consistently getting 50 mbps out of your "480mbps" USB HD because the driver sucks... there's no way you'll call the speed "480".
Plus speed is a fairly vague notion. Throughput+latency+CPU usage are more workable, for I/O. ie for an internet connection, if I'm interested in downloads, "speed" is throughput. If i'm into online games, "speed" is latency... and if any of those is achieved at the cost of 100% CPU use, we've got a problem: I remember my whole PC lagging like crazy (unresponsive UI, skippy sound, burning coasters), in the early days of USB2, when I was doing heavy USB I/O. I switched to firewire.