Google Reader is the back-end/syncing platform for many desktop and mobile feed readers, so everyone who uses those apps suffers from this as well. It's especially useful for feeds that update frequently, because if you go offline for a period of time you end up missing out on content, especially if their feed only has the 15 most recent items. Google Reader is constantly downloading and storing those items, even when you're offline, and syncs them with your client when you reconnect. (Plus if you read RSS on both desktop and mobile, it keeps your read items in sync.)