I think the confusion is that I was specifically referring to the USB port on my hdd enclosure being redundant if the SATA port were eSATAp that accepted USB, whereas you are talking about the ports on your computer, no?Yes, that is a pure eSATA port, not the eSATAp.
"If all eSATAp ports accept a USB 2.0 cable, then there would have been no need for them to put a separate USB port on the unit, either."
Not necessarily. In addition, there are other USB devices that may be required at the same time, such as a mouse, an external keyboard, a thumb drive, etc., etc. My T510 has 3 USB 2 ports and the one eSATAp. All are used.