I suspect most clients will never be comfortable with "designing in the browser" for exactly the reasons you state. It does come across as amateur. There is a

I suspect most clients will never be comfortable with "designing in the browser" for exactly the reasons you state. It does come across as amateur. There is another reason this wouldn't work for most projects. Many, many projects are not just web based. They are part of an overall campaign that includes assets for all different types of media, especially print. Designers have to create assets for all potential media in the campaign, designing in the browser would be duplicating work. However, if all you're concerned with is a pump and dump web product, then this approach may have merit.