Cheap shot, and wide of the mark.
You could equally say "England are a very strong batting lineup - no batting line-up would average 52.1 runs per wicket since the start of the year (including said 51 all out) unless that's the case."
For the record, here are England's Test scores in addition to the infamous 51:
600/6d, 569/6d, 566/9d, 546/6d, 377, 318, 279/2d, 237/6d, 221/8d, 32/0, 7/0
To me, that suggests that the 51 was the exception rather than the rule.
I'm not suggesting we won't get murdered by the Australians (although their inability to bowl my county side's fringe players out doesn't exactly send shivers of panic down my spine) but I just think that basing your critique of a batting line-up on the basis of one innings is a little unreliable.
When Eng played that first test, they were basically in the midst of a downward spiral that resulted in them sitting pretty close to the bottom of the test rankings, i.e. they weren't very good at all
Since that time, they have played a number of matches.
For the balance of the series in WI, Eng played on pitches that could best be decribed as bowlers' graveyards and so any performances there have to be taken with a grain of salt.
The 2 teams then moved onto Eng and the WI bowling/fielding performances in favourable conditions were so bad that they had to be seen to be believed.
Whilst there is little doubt that the attitude/confidence of the English team has improved markedly since the nadir of that 51 (and that's half the battle!), IMO the jury is still well and truly out on a number of their batsmen
In fact, until proven otherwise, the only English batsmen that I have real confidence in (i.e. potential to average 50) are KP and Prior.
Strauss and Cook - will get a real test from Johnson (who is excellent against left-handers) and both still exhibit the technical flaws that have plagued them for some time
Bopara - does not look like a 3 to me as he doesnt cover his off stump
Collingwood - very hit and miss these days
Flintoff - will need a major renaissance as he looks to have completely lost it with his batting
Having said that, it should be a very competitive series as the Eng have a strong bowling attack and the Oz batsmen have hardly been covering themselves with glory either