This idea is a conspiracy theory that has been completely denied by Blizzard. It was explicitly addressed during a developer QA three weeks ago and you can find more information about it on
wowhead. MMO-C had it on the front page too … feel free to dig back through the history if you want to see it there.
And not only has Blizzard clearly and emphatically denied the false rumor that outdoor mobs scale with player item level at 120, you can test it yourself and see that it is utter nonsense.
To be clear, I am posting this for the benefit of the genuinely confused, not to argue with the conspiracy theorists themselves ... because that would be pointless.