It's not the same thing as with plain HTML pages, for here the structure is much more complicated, so the URL's for both the link and the image are much harder to find, isn't it so? Therefore making something like that in plain (or WYSIWYG) HTML is no good option.
On the other hand it should be relatively easy (not for me though

I'ts not that I'm sitting and trying to find what's missing in phpWCMS. In fast I'm (slowly) building my site and there I would like to give people lots of things, mostly ebooks, for download. So there should be lots of clickable covers - enything else is unnatural...
Another use for this format would be banners, buttons and such, though it's not so important to me right now. But please, let somebody implement this - everybody will profit.