>> Does ANY app have interactive sweep?

I suppose you can do it in Houdini, as you can build and animate your own parametric tools. Maybe the 3dsmax stacking system allow this, but I'm not sure.
I don't know any other nurbs package than MoI :)

For the interactive tube, modo has something like that, only polygonal tubes create from 'a through points' kind of curves ... but it's not very handy, a 'control point' drawing method is much more natural (at least for me), and combine with the straight snap I can draw really natural wires/tubes in MoI. More over, not offset snapping in modo either for the tube tool.

I think we can allready forget the interactive sweep stuff. I just did a quick test in MoI, interactively change some curve's control points after a sweep (a simple circle as root shape) is allready really slow, and I 'only' have 10 control points on the sweep rail (and I use an angle 35° in the meshing angle option to speed up the process)

So 'just' the OnSurf offset option would be enough :P