A huge number of those are in operations, building the data centers and making them scalable and reliable. They're not supporting or allocated to a single product, they're making possible the platform that all those products run on.
Running data centers takes people, but any significant chunk of 50k? There is huge datacenter in my area, and only ~10 people work there.
This list doesn't seem to include Google's skunkworks projects like Google Fiber and self-driving cars. It also doesn't include Android or Glass.
http://www.google.com/intl/en/about/products/
1000 employees per product (many of them small) seems asinine to me. I could definitely be wrong, but this seems like extremely low productivity. Does anyone have any insights into this?