Yes, that is the game difficulty in general. Every time you clear a floor, the difficulty increases a tiny bit. Birds get faster, Ralph gets faster and spend less time in "angry mode", so you don't have much notice before he starts throwing bricks, and various other little things. The maximum difficulty is at level 48. Now normally if you start from level 1, you might not get to level 48 because you complete the game before (999999 score). Starting from level 16 will make it possible to experience the highest difficulty level. But good luck with that!!!