All aircraft designers try to make the a/c as light as possible. In the case of the undercarriage assembly that means make the legs as short as possible, among other considerations. All the heavies you mention are low-wing with wing-mounted engines, so the length of the u/c legs has to be just long enough to ensure the engines are off the ground at all times (including a bit of wing flex at touchdown) and the rear fuselage doesn't hit the ground at normal rotation on departure. Any longer than that, and it's just extra weight and longer legs to fold into the airframe after retraction. (Note the restriction on rotate rates on things like the A340-600 with the very long fueslage)
I guess the above considerations are so similar on all your widebodies that they all sit a similar height off the ground. But you'll need somebody from Dowty to post here to be sure!!!!!!!!!