[bri3d]

Skyhook absolutely relies on radio signal strengths and other observables and so do Google's location services.

This can be observed in practice as Android tablets and Apple devices with no GPS or cell radio at all can still locate themselves relatively well.

http://www.skyhookwireless.com/apps-enterprise/ has the marketing-bling diagram of Skyhook's use of multiple observables to determine location; even as of 4 or so years ago when I last used their API you sent them MAC + RSS and got back location.