Might it be that the Win7/Vista drivers for the MBA are worse that the OSX drivers?

We see the comparisons: Surface <-> iPad, OSX MBA <-> Win7/Vista MBA

Surface has different architecture than the iPad, so the battery difference is easily explained, and maybe driver support is just less than stellar, meaning HW isn't as efficient and/or doesn't scale back quickly enough?

I had an Asus laptop some years ago that would last 3 hours under Vista, and would be dead in the water in 1 hour under Ubuntu. I think it was either GPU or CPU scaling or both that wasn't supported in the linux drivers I was using