Google does offer Windows laptops, including to engineers. I had one for a while. It made a perfectly adequate thin client to my Linux workstation and made debugging in Windows browsers significantly easier.
They didn't during my time. But my department didn't do anything that had to do with Web... also, we got into Google through acquisition, and the company originally started with developers working on Linux and rarely Macs. The IT wasn't really very selective about it, so there was a guy who wanted a Windows laptop, and they gave him one since they had licenses for the HR / sales etc. people, but he quickly gave up the idea.
So, by the time we became Google, nobody really thought about it as a viable option.
