The ability to support a particular OpenGL standard is dependent on the hardware (software implementation aside). It is not something that Apple can choose to implement on less capable hardware. That's almost certainly why both Windows and Mac are running OpenGL 2.1 - OpenGL 2.1 is all the hardware will support.

On the other hand, based on your report it appears that NVIDIA has invested more effort in the performance of their Windows driver than in the performance of their Mac driver. Given their economic interests and the fact that many people using their hardware under Windows are NVIDIA customers whereas the vast majority of people using their hardware are Apple customers, it is hardly surprising that they would do so.

I will point out that for people who give a high priority to 3d graphic performance, there is little reason to select an Apple product - a meaningful range of hardware options simply does not exist and the drivers simply receive less attention. Keep in mind that one of the major differences between workstation class graphics cards such as NVIDIA's Quadro and gaming cards is the quality of the drivers - the same GPU's are often used in both segments with driver performance justifying much of the cost premium workstation cards command.