Thanks for the replies, yes the A 380 isn't especially pretty and when downwind for 09L as has been the case this week they look positively odd with the stubby fuselage and giant tail masking their size.
I have flown on one a couple for times and it was very impressive in terms of quietness , smoothness and excellent cabin environment conditioning.
Going back to my question , yes the comparison with the twins is a good point and a valid and I am sure accounted for some of the difference but I think the last post about he A380 not being at its best low down is a large part of the answer especially as they seem to have caught up with the 'normal ' SID climb by the time they had got out to the Bagshot /Camberley area. With your location Mr 10DME I guess you get to see a lot of them too
if you happen to be around LHR when one departs it is quite interesting sight because it is incredibly quiet and once airborne seems to accelerate very quickly but not climb -so if you live in Feltham when LHR is easterlies you must get a seriously impressive view because the A380 wing really does blot out the sky.
thanks to all
PB