No. Powell is a slightly common name. Janey also had the last name "Hagstrom". Her last name is probably filler, due to Janey being a fairly minor character as well as a satellite character to Lisa (as a friend, but not a very good one). As seasons went on, she was pushed into the background, just to confirm time and time again that Lisa has no friends. Yes, it indeed shrunk Lisa's world. Herb's last name is major, since it confirms who his adoptive family is. His now defunct company was even named Powell Motors (the only name he knew before discovering that he was a Simpson).