You know those add-ons are enabled by Blizzard, right? That there is a published API on how to call functions from Lua code thst let you get all kinds of information about NPCs (RareShare), auction pricing (TSM), the user interface (Bartender4), and most importantly, combat (DBM), and a host of other things.
Blizzard could kill it all by making the API private/inaccessible, but they made it public. They essentially encourage users to develop their own Lua code as an add-on to enhance their gaming experience and to share their personal efforts with the community.
Pretty difficult to get behind a claim that add-ons are cheating when their very existence is enabled and encouraged by the game developer.