What surprised me most from the ruling was how it took the legal doctrine of idea-expression dichotomy and twisted it into absurdity, hinging on an implicit argument that a game design essentially serves no utilitarian 'function' or 'purpose'. Core mechanics or essential gameplay rules like the tetrominoes or the 10-block width of the playfield are thus marked 'expression' or 'arbitrary flourishes', leaving a vague, unidentifiable abstraction of a falling-blocks puzzle game as the only unprotectible set of game rules that form its 'idea'.
Xio was free to design a puzzle game without tetrominoes, or downward+lateral+rotating movements, or a 10x20 playfield, and it would still 'function' just as well (that is: not at all, it's just a game). A chess game developer is equally free to design a strategy game without an 8x8 board or the knight's distinctive L-shaped movement, but it would no longer be chess, it would be rules for a completely different game.