A380 Economy seat layouts

[castie]

I am a bit puzzled by this question so maybe someone can help.
Taking the Economy stats for A380's from seatguru I get the following results for seat width.

Qantas 17.5
Singapore 19
Emirates 18
Malaysian 18
BA 17.5
Lufthansa 17
Air France 19

So here comes the puzzling bit...they all operate 3-4-3 layout so why the big differences in seat widths?
Surely if AF and SQ can give 19 then the rest should have basically the same width as its the same aircraft.

Is there some reasoning behind this? I do realise that seatguru dimensions may not be 100% accurate but I am assuming they are at least close.

[TABLE="class: seat-list"]
[TR]
[TD="class: item2"][/TD]
[TD="class: item3"][/TD]
[/TR]
[/TABLE]

 

[mannej]

The extra width is taken from elsewhere (re the aisle).

I didn't think the QF seats were particularly narrow, but each to their own.

As an aside, the seat width is the last thing I'd be worried about on AF...