It's a classic Grail theme, as is the additional story line of the Vengeance Quest. The player's character in Baldur's Gate is orphaned at the start, and must find his father's killer.
It put me in mind of Jessie Weston's famous work, From Ritual to Romance, which influenced T.S. Eliot's poem, The Wasteland, and which is Colonel Kurtz's bedside reading in Apocalypse Now.
I recall the old Doubleday Anchor paperback you used to see in campus bookstores.
I think I still have a copy of this edition at home. I wondered if the library owned a copy. I was a little surprised to see that we did: Princeton UP's 1993 edition under the Mythos imprint, with a foreward by Robert S. Segal.
I found it at 809.915 WES. I turned to the cataloging label, and saw that I had put it in the Bookmobile collection in 1996. I used to send enduring works like this up to the main collection when I took them off the truck. It has gone out 31 times since then, most recently in December 2009.
Strange to think that elements of the Grail myth are key to the appeal of so many "quest" RPG's played by millions today.