This has everything to do with the way the TV is hooked to the converter box. If you are hooked up via HDMI or component video cables, you can watch in HD if your TV supports this. If you are hooked via coax or composite video, you are always watching in SD. Remember, you are limited to the abilities of both your TV and the box you have.
Correct me if I am wrong but that text box that BHNtechXpert shows the best resolution available from the box you have no matter how it's hooked up and how old the TV is I am pretty sure.