Google doesn’t indicate why they chose The Prado specifically but it is certainly a well-respected museum with the works of some well-known painters from the 12th to 19th century. From what I can tell, Google created digital images only of their paintings and not of any of the sculptures which makes sense given the technology they’re using. The Google Maps version of this project is scaled down in almost every way. They only have a selected group of images and the metadata is limited to the name of the painter and the title of the painting. Google Earth’s display provides much more information including the date and some of the source information.
I think this is an incredible project. To have such high resolution images of these paintings available to everyone with Google Earth is amazing. As you zoom in you can see every detail of the photo, getting much closer to the image than you would be able to even if you were at the museum. Some people might object to the way the images are stitched together, arguing that data could be altered in some way during the process but I think overall this is a really advanced project. I’m blown away every time I see “14 gigapixels” though.You can read a bit more about the project on ReadWriteWeb.