As much as I'd always rather have a designer that does HTML on the team (for the sake of quick and agile adaptation), vs someone doing just photoshop, I believe that a good analogy would be architecture. Architects have fairly good understanding of specifics of various materials, their performance as well as associated costs. Still all projects are always reviewed by a 'construction engineer' who converts the architectural vision to workable implementation (that is then on passed to production teams). Taking that example to the online world - designers should understand all of the mechanisms that they will use in the design, and communicate their vision to someone that will implement it. They do not need to actually code it, because following that logic - being a product manager for LinkFindr (and CEO, and business person etc..) I should never allow any designer to spoil my vision with her artistic view, and just storify, mockup, PSD and then code it myself. It takes trust and good communication to split up work in the team, but as Ford proved a couple years ago - when you're running at scale, there is no other way.