Why is the article full of JPEGs?

Article:		Google Your Desktop
Subject:		Why is the article full of JPEGs?
Date:		2004-10-15 08:51:16
From:		sceen1

I really wasn't expecting to have to load over 100KB for each screenshot I clicked on! Why are the images not in PNG format, where they would be at most 20KB or so for full quality?