Amazon Kindle Charging Technique

They do not ship a charger with Amazon Kindle in India. One has to connect it to a computer's USB port in order to charge it. I do not like it very much, because I do not want to switch a computer on solely for the purpose of charging my Kindle. After all, I bought a Kindle so that I could read books without using a computer. Since I had no option, I charged my Kindle on my laptop. A problem with that was that the charging would stop when I shut down the laptop. Then one day I connected it to my desktop, and found that the carging continued even after I shut down the desktop, but did not switch off the mains supply. Yesterday I connected it to the USB port of the desktop, and switched on the mains supply, but did not boot the desktop. Even then the Kindle got charged. Not only did it get charged, it showed a green indicator when the charging was complete and then shut off all indicator lights. Thus a desktop PC is a charger for a Kindle, even without booting it. I wonder if the makers of the Kindle know this. After all, if they knew, they would said so in their manual.