They look higher res but really they are just zoomed out. Whenever you see the original 1997 game assets extracted from the game you see them that way. However, only a small portion of each field image is shown on the screen at one time (where you are walking) so the result is far more pixelated than looking at the whole thing on the screen at one time. For better resolution, you'll have to install mods such as ones that up-res backgrounds (perhaps
http://forums.qhimm.com/index.php?topic=12260.0 ). Some backgrounds have been recreated (see Team Avalanche category of the forum) but there are so many backgrounds in the game that recreating the models can take years with a small team even if they work on it consistently.