Back in the day, the warez/emulator group Damaged Cybernetics included its members to use a standard page background and images, at standard URLs. That way, users who browsed through their sites will have cached the images and need not load them again when viewing another member's site. In the days of dialup this was a big deal.

If every server knew how to properly cache even static assets, more sites would handle a HN traffic surge.

That may work for a high-traffic site like Google, but what about sites that aren't in the Alexa top 10 (or even 1000)? ;)