Isn't this just the prospective illusion for the 3-D effect?  Does XL2007
have the functionality that XL97 has of altering the Elevation and Rotation
when you right-click on the chart and select 3-D View...?  When I do that in
XL97 with your figures and set the Elevation and Rotation to 0 it proves
that the columns are the right size.

Nick,

I think it appears to fall short of 14002 because of the viewing angle.  You're getting
parallax.  Try this:

Click the background part of the plot area, such as between gridlines.  There should now be
handles in the 8 corners of the 3D plot area.

Click one of those handles.  Nothing will happen, but it's just something that seems to be
needed.

Now drag that handle slightly.  The plot area should move around in 3D space.  Hold the Ctrl
key as you drag.  You can move it so that you're looking more directly on to the plot area,
instead from somewhat above as your currently are.

To make it more apparent, do this:

Set your Y axis to a maximum of 20,000 (Right click one of the Y labels and choose Format
axis - Scale tab).

Change one of your cells you're plotting to 20,000.  Now the associated column should go to
the top of the plot area.  Change the angle (first part of my post), holding Ctrl as you do
so.  It won't appear to go to the top of the plot area (20,000) while you're viewing from
above or below.

I don't think the 3D view was meant for accurate scale work.  It's more for comparative.
And just pretty.