Despite their recent 'fighting form', McLaren knows full well that Red Bull is still the team that is aerodynamically ahead of everyone, especially when it matters blown diffuser performance. It is therefore no surprise to see the British team to simply copy some changes on the diffuser of the Red Bull RB7.
RBR recently replaced the common gurney flaps along the upper edge of the diffuser by small wings, proving a more effective method to help create downforce at the rear end of the car. The small wings not only help extract air from out of the diffuser, but also directs air upward while creating less drag than the common gurney flaps.
McLaren have been running this change since Singapore, whereas Red Bull ran it a few races earlier. The most obvious difference though is that Red Bull's version extends to the outer sides of the diffuser, whereas on the McLaren the vertical fences are still closed gurneys.