Langer also had the stability and the experience of the Australian middle order to fall back on. There is a serious, serious difference between having (Steve Waugh who had something like 50 tests on him at the time) and Allan Border (who had well over 100 by this point) coming in after you than having 3 out of Ian Bell, Ravi Bopara, Paul Collingwood and Prior.
AB was a walking wicket by that Test and Steve Waugh was on the verge of being dropped having not been able to establish himself at 3. Have to ask, did you see the series? The Aussie batting was a mess. This was after AB and Mark Waugh had scored tons at Melbourne. It was amazing how quickly their form deserted them when the WI started bowling well. JL walked into the side right in the middle of a bunch of guys playing terribly with a couple (Taylor, the Waughs) playing for their places.
And thats not even considering the fact that Taylor and Boon were opening at the time that there was enough proven and experienced players in that side to take that risk.
I take it you didn't watch then. Taylor was dropped after the Adelaide Test because he'd barely scored a run. Only Boonie really looked likely to score serious runs against that WI attack.
I'll give you that the experience of the Aussie top order was there but they were absolutely on the back-foot by that Test and JL walked into a very, very unstable top-order. Materially, I don't think there's much difference in terms of pressure that a first-gamer would face walking into that line-up vs the England one for the Oval.