The part I find most annoying is their guides, written in Lua, are a database that requires their addon. That's like getting GatherMate2 for free, but getting charged for GatherMate2_Data. Thankfully, that is not the case with those two, but that is very shady business.
I would totally understand if they gave you the addon, full database for free, and charged for the physical book, perhaps having the inevitable errata be accessible on their website only for people who bought the book. But I feel both the addon and the DB should both be freely available. That, of course, is just me.
About paid addons and their timeframe, The policy was put in place for patch 3.1, updated May 2009, and again November 2010. Here is the US official forum link.
http://us.battle.net/wow/en/forum/topic/1021053914