Not only is it generic, but it is a word that has a long history of being used in the name of games well before "King" existed as a company:

http://www.mobygames.com/search/quick?q=saga&x=0&y=0

If Nintendo were to release a Mario and Luigi Superstar Saga sequel, would King be so "gracious" as to allow them use of the Saga term?

This whole situation highlights how ludicrous IP law has gotten in the past decade.