The web is a world of constraints, the materials of HTML and CSS flex and give in ways that encourage particular styles. And being able to understand and bend within that scope is what makes a design feel native. Designers who work directly with the materials rather than through simulated environments like Photoshop are at a distinct advantage for making that happen.
If you’re working on a Flash game or a media campaign to introduce a new watch, you can afford to disregard that advantage. That’s when the graphical prowess of a completely blank canvas, sky’s-the-limit approach is exactly what you want. You want dazzle and glitz. Making something that’s native to the web doesn’t really matter.
But barring that niche, designing for the web is a lot less about making something dazzle and a lot more about making it work. The design decisions that matter pertain directly to the constraints of the materials. What form elements to use. What font sizes. What composition. What flow. Those decisions are poorly made at an arm’s length.
I’ve worked with many web designers in the past who only did abstractions and then handed over pictures to be chopped and implemented by “HTML monkeys”. It never really gelled well. The things that got strong attention were all the things that Photoshop did well. Imagery, curvy lines, and the frame. All the around stuff, never the it stuff.
That’s why all the designers at 37signals work directly with HTML and CSS. We simply don’t consider designers who don’t get their hands dirty with the materials relevant to the kind of work we do.
If you’re a designer working with the web who still doesn’t do your own implementation, I strongly recommend that you pick up the skills to do so.