If you read the article (and others) you'll see they're not retconning - least not in the sense that you're thinking of. Off the top of my head, the "retcons" I can recall reading about are:
-Changeing the layout of Stratholme to match WoW, and changing its architecture to be less 'random' (the whole 'fish fountain' example)
-Adding a scene that shows Arthas resurrecting Invincible, to explain where he gets his horse in the Scourge campaign
-Adding extra material for Sylvanas and Jaina
-Giving Jaina extra lines in the Horde TFT campaign, to better acknowledge her grief over her father's death
-Addressing the issue of the draenei (this is a bit vague, but it'll probably be along the lines of acknowledging that these are Krokul draenei)
It's "retconning" in the same way that REmake retcons RE1. There's plenty of stuff added, but the core of the story remains the same.
Meiam said:
Like at the end of Rexxar campaign Jaina version of the alliance is slowly becoming friendlier with the horde just to have all of that ignored when you start WoW.
Jaina's not a major figure in the Alliance when WoW starts. I'm also not sure where it conveys the idea of the Alliance becoming "friendier" to the Horde when the people of Theramore have had to stand aside and let the Horde deal with Proudmoore. This is touched on in 'Cycle of Hatred', which, if anything, makes things worse. Plus, there's various other things that contribute to deteriorating relations by WoW (logging in Ashenvale, Alterac Pass dispute, issue of Lordaeron and the Forsaken, the issue of Northwatch, etc.