I think you might have misread the table. Windows 8 64 bit looks to have about a 1% lead on the four versions of Mac OS listed:
Windows 8 64 bit 4.25% +2.40%
MacOS 10.8.2 64 bit 1.49% -0.11%
MacOS 10.6.8 64 bit 0.78% -0.20%
MacOS 10.7.5 64 bit 0.72% +0.03%
MacOS 10.7.4 64 bit 0.27% -0.27%
Comments
I think you might have misread the table. Windows 8 64 bit looks to have about a 1% lead on the four versions of Mac OS listed:
Edit: Formatting