A significant amount of the data is freely available data produced by the U.S. government(s). The issue is processing it into something nice.

The level of coverage that can be done with that data can sort of be inferred from this post:

https://www.mapbox.com/blog/mapbox-satellite/

(they basically processed landsat imagery to get large scale data for the entire globe, and free imagery of the US gets quite a bit finer scale)