"Does anyone have a theory as to why Williams stayed out of the vector game
arena?"
Two guesses:
1) Williams got into the video coin-op arena pretty late (not counting TV Ping Pong..)
and had hits on the raster side (Defender,Stargate, etc)
2) It doesn't seem like there were many contract game companies doing vector gams
(were there any? Cine, Atari, and Sega were all in-house designs)
Williams bought all of their designs (Vid Kids, etc..)
..at least that's my guess
Aztarac and Omega Race are the two odd-balls (and Omega Race was a copy of Asteroids)
