BootCamp isn't emulation, its installing Windows next to OS_X, same as I will dual boot OS's on a windows tower. However the main cause of the low framerate on the mac air is largely due to the graphics, the HD 4000 is sharing some of the system RAM which will be DDR3, much slower than dedicated GDDR5 graphics card RAM.
You should have seen some increase in fps with Beta 2, and as Teabone said, Lee is still working for FPS on older and non-dedicated hardware