Those shots are not compressed. Its upscaling and grain filter that unfortunately diminish some details and clarity.
Are you sure about that? I just checked and it's indeed .png, but I don't know how if they were converted from .jpg to .png.
The top one looks like it could be from a FMV, because a lot of detail seems lost. My only explanation is that the loss of detail is because of video compression.
Unless the game uses a Blur AA solution ?
I figured there was a lot of detail because I have seen a lot of high res screenshots, I'll try to find some for comparison