Well, 37signals talked about that some years ago.. I am a front-end developer with some UI skills but no design skill at all so I maybe a bit flawed but..

It all comes down to what you are looking for, I never saw a designer as good as a front-end developer doing html/css + js in real life (of course there are a couple of rockstars on the web).

They always have more a trial/error style than good code by design. Plus with web apps going more and more front-end side, you need people that do great html/css/js if you want a great working app.