They did not change the whole grunt model for a game like 343 did. Also you can't be pleased if their skin was different in a game from another. Unless you were scoping the grunts as soon as you started playing H3 and getting mad about that "huge" change. There is maybe a huge gap between grunt models from Halo 1,2,3 even Reach in comparison to Halo 4's. Heck there's even a pic in this thread showing that. Halo 4's grunts are supposedly to look like they were described in first place, but books and games are different. Like Movies and Books, you can't have every detail that the book offers into a digital movie and in this case a game.