Just in case there’s any doubt :-)
The designer adds something important that technical experts may neglect—the ability to bring grace and elegance into forms and devices that are humanly engaging, often exciting and sometimes unexpected. Designers add marvel, and that can make a product more deeply usable, reaching beyond the prosaic or pedestrian.
— Dick Buchanan, Good Design in the Digital Age
Update: Jamin Hegeman, MDes 2008, posted recent thoughts by Buchanan on this topic here: http://jamin.org/archives/2006/why-designers-are-valued/