As for the untapped potential in the web medium: it's a bit naive to think that understanding CSS transforms will truly, fundamentally, change a way the designer decides to present a piece of information.
Where would you draw the line? Why shouldn't designers know Unix and TCP/IP programming as well, since those are both part of the medium they design for.
I beg to differ. Clothing designers know their fabrics. Blacksmiths know their metals. Leather makers know their leathers. Architects know their building materials. And yes, car designers and iPhone designers know their mediums too. I could go on.
I guarantee Jony Ive can tell you all about the capabilities, tendencies, and limitations of the glass, plastic, steel that comprise the iPhone. You think car designers don't know precisely how steel can be formed and about the processes that form it?
But yet web designers don't need to know HTML and CSS. It's by far the easiest medium to know of all those I mentioned. I agree with another poster: It's lazy.
It goes without saying that designers should know how people will interact with their products, but knowing how to code is just one way to do that, and it is not the only one.
It's because to design for any medium you must understand its capabilities and its tendencies. Those too exist on the web, even if they are easily forgotten -- the web pages's tendency to scroll; its capability to be resized; its capabilities of being receiving new content and return visitors.
There is so much untapped potential lying dorment in the web medium, passing by all of those who resist to use HTML, CSS, and a browser during experimentation. It's depressing.