From a user standpoint I would agree with http://www.bythom.com comments
about the 200mm focal length of the 18-200 Nikon not being all that useful
on an everyday basis compared to the elephantine/SUV size and heft of the
lens.
Whether or not having a 16 or 18mm focal length at the wide end makes any
real difference is a matter of personal choice.
How many people have 10-20ish wide zooms and actually use them with any
frequency?
One thing that is way too underemphasized in many discussions of these long
consumer zooms is their inescapable problems with vignetting at their wider
apertures. This is far more apparent in images than linear
(barrel/pincushion) distortion because you will see it in, for example,
every landscape that includes expanses of sky shot at the wider apertures.
Since most of us, particularly when travelling, default to the otherwise
accurate program exposure mode these lenses end up producing a lot of sharp
and contrasty images with darkish corners.
Vignetting is such a ubiquitous problem with modern zooms that I presume
this is why Adobe includes correcting filters for vignetting in both the raw
converter and desktop.
It is not always practical to shoot at f8 or smaller apertures even when
shooting in aperture preferred mode.
Hence while these lenses may have a maximum aperture of f3.5 they
functionally have maximum apertures of f5.6 or f8 in outdoor use or when
shooting against light colored backgrounds, not much different than a 1950s
era camera.