Just in case there’s any doubt :-)
The designer adds something important that technical experts may neglectâ€”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/