It matters less, but more because data tends to land in 'bursts' when connectivity is poor, so unless the image is massive, you're less likely to see a partial image.
I think you missed the point. In cases of poor connectivity, you're not receiving (eg) 200 kB gradually over 10 seconds, it's more likely that you get nothing for 10 seconds then 200 kB lands.
This is why progressive rendering doesn't work in reality in the same way it does over a simulated connection.
