The first two screenshots show the performance of the Seagate drive attached via the motherboard's onboard USB 2.0 controller. It's easy to see that the performance of the drive is limited by the USB 2.0 interface. If the interface wasn't a bottleneck, the shape of the plot on both graphs would be a curve, since the speed data is read/write changes depending on whether the data is near the inner portion of the drive platters, or close to the outer edge. But with these two graphs, we have flat lines.
Switching to the Vantec USB 3.0 ports, the Seagate drive can stretch its legs. Even at the lowest speeds, the drive is able to be read/written to at over 60MB/s. This is nearly double the performance compared to when the drive was connected via USB 2.0. The shape of the plots resemble what you'd see when the drive is attached to a SATA interface, where the interface isn't the performance bottleneck.