Just stumbled on an old Science 81 magazine on eBay. I have this same edition in my book collection. It brings back fond memories as there is a good 9 page article on Vectorbeam Star Castle versus Williams Black Knight.
http://www.ebay.com/itm/Science-81-V-2-2-Mar-1981-Lucy-Fossil-Blind-Sight-Penny-Arcade-Clipper-Ship-/200679258684?pt=Magazines&hash=item2eb96a7a3cThe article starts with "Video or pinball? Can a two-level, deep-voiced Black Knight with Magna Save and a sinister laugh conquer a Vectorbeam Star Castle with pink energy rings, smart mines, and an all-powerful space cannon? Get out your quarters."
There are some nice photos of Wynn Bailey (Star Castle) and Steve Ritchie paying the white-wood BK. Couple of other photos shows BK prototypes and the Williams production line with wired playfields.
You can see in this article why BK was such an important pinball for Williams. "Americans spent almost $3 billion in quarters to play outer space video games in 1980, $1 billion more than on the space shuttle." By the way, those dollar figures would be 4 times in today's value.
Another interesting fact in the article "....The first Black Knight on location in Chicago collected $500 in one week, four times more than any other pinball machine in the arcade and slightly more than any video game."
Some words from Steve Ritchie in the final paragraph of the article:
"Black Knight could be number one. What I've learned this year is that if you make a powerful game, you can do just as well as video. Before the show I felt obsolete. I don't anymore, and I'm glad, because I love pinball and I don't want to see it die."
Fast forward 30 years and although penny arcades are almost dead, a good pinball still arouses plenty of interest.