Size vs resolution
This is an example of a REALLY big screen
<img src="http://nhoffman.gallery.netspace.net.au/albums/OZ-GP-2oo7/IMG_3454.jpg>;
You can actually SEE the pixels. If you don't stand back, it's useless.
The trick with screens is to trick the eye into NOT seeing the pixels (blur them spatially, or with movement, is usually a good way)