>>26585480We've seen tall grass in the new trailer. Pic related also shows several patches of grass. There's no particular reason it needs to show up on the distorted, fish eye view of the region map.
Now, what one might question, is why the grass seems to off the path in these routes. It might just be that we've only seen the clear bits so far because they haven't decided to show us the player encountering wild pokemon yet. Pic related does show a more grass crowded path splitting off at the bottom. It may alternatively be that routes are largely clear of grass you need to go through and that's something people will begin to bitch about as it becomes more apparent.
I guess we'll see as more of the game is revealed.