A nice analysis of why Lego has seemingly lost interest in the Mindstorms line:
Lego launched the Lego Mindstorms line of programmable toy brick construction sets with a lot of fanfare back in the fall of 1998, but in recent years the company has lost all enthusiasm for the Mindstorms line. For several years now, Lego has not introduced any new Mindstorms sets, and the company has discontinued almost everything in the Mindstorms line apart from the core Robotics Invention System (RIS) set. Sadly, even the RIS is not faring lucky as it has not had an update since 2001. Lego seems to have relegated the Mindstorms line to niche status and frozen its development.