Obviously a simpler website could be scaled with responsive design to work well on a small device but it but I think for many sites a separate mobile version is the best idea.
Anyone want to weigh in on this (friendly) argument?
I've been looking at this problem, and my answer is that, up to a point, each view is right, in it's context.
Look at the glossy, animated, automobile sites. Can you scale that to fit on a 320x480 screen? No, of course not. If your graphics are 800x600 you need a display at least that size to show them on. And downloading big animations is a joke on mobile systems. 3G is pretty slow in broadband terms. You do not have the bandwidth. Is there a place for big glossy sites on the web? You bet you. The question is, do the auto manufacturers want to also reach a mobile audience? If so, they need separate sites.
But what percentage of sites are big glossy corporate vehicles? There are a thousand sites that could work well on mobile and PC devices for one that really needs separate sites, but right now they do not. Why not? Well, I suggest that there are a host of reasons, but the main one is an over-reliance on technical, rather than pragmatic, solutions:
Historically, mobile devices had screens of the size of 160x240 or thereabouts. But they did not just develop different sites fo them, they invented different rules. Why? I do not know. All I know is, it was a blind alley, leading nowhere.
More recently there has been the development of mobile responsive sites. These rely on a dialogue that:
a) The older low resolution devics do not understand.
b) The newer mid to large resolution devices do not need.
The division between handheld devices and traditional screens is blurring. My Symbian phone with a 320x240 screen responds as a "handheld" media device, but my Android 320x480 phone responds as a "screen" media device. What sense is there in that? A page has to be displayable in a width of 320 pixels on both. So the media distinction between "screen" and "handheld" devices has already been compromised.
So the solution is not technological. It lies in crafting sites to fluidly accommodate screen widths from 320 pixels upwards. That can be done in HTML4 and CSS2. The clients need to decide whether a fluid 320px site meets their needs. If so, and I would suggest that in the majority of cases it is so, that can be done with fluid design techniques. But, by exception, separate sites are needed.