When I save an inkscape document as a pdf (cairo), there is banding in the gradients when viewing the pdf (at least when I view it with foxit).

However, if you import the svg into scribus, and then use scribus to export as a pdf, it works perfectly. The gradient itself becomes vectorized in a true fashion.

Unless it's changed since 0.46 (I currently only have the dev version installed), the gradients saved in a PDF by Inkscape is true vector--the banding could be the result of multiple factors, but since it's vector is unlikely to be Inkscape's fault. To test for yourself, re-open the PDF in Inkscape and attempt to edit the gradient. Scribus may be getting around the banding by rasterising the gradient and applying a dither. Again, if you open the PDF in Inkscape you'll be able to identify if I'm right or wrong about that.