Ask HN: Adblocking using /etc/hosts

It is well known that AdBlock Plus extension is a memory hog. It gives many features like disabling the extension on some sites, etc but I never use this. Everytime you enter a domain name, it is converted into IP using DNS Lookup. /etc/hosts can be used to map all the ad sources to localhost. This seems like a much better way to do it. I wanted to know if there is any particular reason people don't use this method ?