Actually it rewards you for nothing, because you don't have to do any sort of play to take advantage or a gaping hole you can walk through that has nothing to do with what you did or they did.
That isn't promoting anything but two people posturing boringly so they don't lose a tower. It promotes even more stale early game because people are less likely to roam or even back because they might lose their tower. It does punish bad play, but it just as much rewards doing almost nothing as well. If this was because YOU (or me, just using the general you) actually did something, I'd be okay with it, but when you can back to buy and still lose a chunk of your turret even to a mid laner, then that is bad design, because you are being rewarded for little to nothing.
Don't forget that not only do you get rewarded for little effort, but in the next patch the minion buff with that advantage gives you an even bigger advantage, and so on. **Riot doesn't want plays to matter, they want games to end quicker, and are trying to take that power out of your hands and have the game sitting behind you pushing you forward to make sure you end. ** Sure it feels like you did something more spectacular than you did, but in reality it is the map winning the game faster for you (especially in the next patch), compared to just you. That is what I'm not okay with.