Bill's right on this one ..If you surface on ICEM or Alias or catia v4 they are b-spline or bezier,or nurb surface...not parametric so they wont update with dimension changes..if you do them in a parametric system than yes they can and will update if set up properly..keep in mind that inside fillet operations can and do fail upon dimensional updates causing the need for freeform surfacing.
we have lots of designers straight out of college who have no idea what true length of line means.You need to know the formulas then the cad will help you tweak them quicker.BTW Iges is not reliable for acurate surface data transfer in my opinion.