That part is true, but its still ridiculously unbalanced. You can have the gears that finishes or farm Act I comfortably. And with the same set up, you can (and probably will) get killed by a regular Wasp within first 5 minutes of Act II. It just doesn't make sense.
Oh...and let's not even bring up the enrage timer. A big "fuck you, go to the RMAH and buy some better gears if you want to progress" to the players.
I know it's fashionable to tie every game design decision you don't like into the RMAH as a gotcha to Blizzard, but it's really not helpful for productive discourse. They've publicly stated their motivation for pretty much every decision they've ever made, and it's always at least reasonable in theory. The enrage timer is there as a final prevention of cheesing the content in lame ways, and as a way of communicating "look, you can't do this, just forget it" to the player so they know they need to change something. Diablo is a gear game - no matter how you get the gear, there will always be the risk of utter failure when your gear isn't sufficient.