I have a group pinned large to my screen and I noticed how poor the image quality is that gets sent down. To me this makes the large tile undesirable on the screen. To push an image at the proper scale dpi wouldn't add much as far as bandwidth is concerned. I hope they fix this on their end. This is not a case of a poor image on the server (facebook), its almost like whatever resizer they used for wp7 was used for wp8 with no tweaks for the new tile sizes.

Just a thought, this was bugging me the other night.