I got a (very cheap) Thinkpad from my university. It had that proprietary Ethernet port. It came with a ThinkPad-branded USB to Ethernet adapter. The adapter came with the laptop and still didn't use the proprietary port!

Now, there is a chance that the university IT which set stuff up before giving it to me, is responsible for disappearing the proprietary adapter. But because the USB adapter is branded with ThinkPad, I really think it's just what it came with.