Should Google Spice Up Their "404 Not Found" Pages?

A Search Engine Watch Forums moderator asked why are Google's 404 Not Found pages so cold and unhelpful?

For example, there is no page on the Google domain over here so Google returns a header status of 404, to tell us and spiders that the page requested is not found on that server. But from what we all know, 404 pages, although sad in nature, can be salvaged.

But creating custom 404 pages, you can help aid your user to find the page he or she was looking for. Google's 404 pages look like this:

Why not put some of the Google Products on the page with a big search box and some sponsored listings? It has to be more useful then what Google has now.

How are Google's 404 pages helping organize the content of the world? I wonder if there is a strategic reason behind why Google may use plain vanilla 404 pages. I can make up some reasons, but I am interested if we can possibly get a plausible explanation from a Googler on this?

Forum discussion at Search Engine Watch Forums.