I am going to steal a little trick I learned from Joel Spolsky and give you a little blog test.  This is a simple fill in the blank.  Designer is to Engineer as Architect is to ____________ .
To see the answer 'magically' appear select the area below with your mouse.

Engineer

Is that a trick question?  Yes Architects and Designers both require Engineering to create their designs.  Of course Architects create building and Designers create products, but they both share the same set of 'tensions' that shape their designs as the picture illustrates.

Some people might take exception with the 'art' element.  I have used art instead of the more specific case of industrial design.  Industrial design has the functionality, cost and ergonomics elements built into it.

Designers are not necessarily engineers, and Engineers are not necessarily designers.