Seeing as how the rope can already do this, I don't see why most other weapons aren't able to shoot when your hedgehog is in the air or sliding. It kind of messes with the flow of the game sometimes.
(eg. When you have 2 seconds left in a shoppa turn with your weapon out, but can't shoot it)
Not to mention that even the aiming crosshair is still visible at all times - leading to the misconception that you can fire it while sliding and falling.
Maybe there is something technical preventing this, please enlighten me on that if there is.