There has been a lot of mis-understanding of the 5MP image captured With the 808, 1020, 1520 & Icon/930. In short the 5 MP image is a much higher quality photo than a normal 5MP image because it combines & averages the pixels from the 20MP image to create the 5MP image. This is taken from the 1520 whitepaper:
"Like the Nokia Lumia 1020, the Lumia 1520 also uses Nokia proprietary oversampling technology, combining the pixels in the image to generate incredibly beautiful and sharp pictures.The Lumia 1520 uses similar oversampling technology as we have in the Lumia 1020, although the oversampling ratio is higher in the Lumia 1020 (which is 1:7, since the Icon/930 is 1/2 the MP I assume it's ratio is 1:3),” says Juha Alakarhu, the head of imaging technologies at Nokia, with a smile in his face.
“However, we have actually significantly improved the capture algorithms since the first software version on Lumia 1020, so for example, the noise levels are further reduced in the new algorithms. Just take a look at the 5-megapixel oversampled photos: they are sharp, natural, and low noise. The oversampling technology really makes this 20-megapixel sensor ‘alive’”
“As we said a couple of years ago, it’s not the amount of megapixels but how you use them.”
Read this very thourgh review of the 1520's camera (same camera in the Icon/930) by real photgraphy pros here:
Introduction: Nokia Lumia 1520 camera review: Connect