I don’t know why this is mistakenly repeated so often. Harriet Miers was nominated for the seat that was subsequently taken by Samuel Alito, not by John Roberts.
I think this gets repeated, because people forget, that Justice O’Connor resigned, and very soon after that Justice Rehnquist died, so that “W” was filling two Supreme Court seats almost simultaneously.
So people get confused as to who replaced whom on the Supreme Court at that time.