World of Warcraft is very old, by videogame standards. It was released in 2004. And about every two years, Blizzard releases a new expansion to update the game. Typically expansions don't really replace content, but it does displace it, and changes to mechanics and player abilities are indeed permanent and "retroactive". And in 2010, the Cataclysm expansion DID actually replace the old content from the release game.
The leveling guides on my site are essentially speed leveling guides. My leveling guides are the same guides I use myself to speedrun to 60 on new servers to get 60 server first. I list many occasions where I tell the player to "die on purpose" to go faster. I tell the player to skip certain quests, because some quests are just not worth the time/XP. I list tricks and shortcuts to go faster so you can reach level 60 much quicker. I am still constantly going through them over and over again perfecting the guides to make them faster and easier to follow. For the most part, the guide can be followed without the need from other player's help, as the whole guide was made from a solo run anyways. Although I do list quests that can optionally be done if you have a group.
Check Item's Vendor Price before posting it on the Auction House - Selling items on the Auction House below their Vendor value is a common mistake. Avoid it like fire, and always make sure that you are not losing Gold on your Auctions. If you plan to sell an item on the AH for a price just a tiny bit higher than its Vendor value, you might be better off just vendoring the said item (this will allow you to avoid the risk of losing an Auction fee if your Item doesn't sell).