While I am willing to concede that different markets may be different, I also think that much of the objection is based on some programmer-types arguing other people are stupid and literal (“I would never be fooled by a box shot, but other people, who are not as clever or savvy as me, might be”), or simply behaving in an unnuanced, even mildly Asperger’s, type of way requiring everything to be just so. BTW, if you have that tendencies towards that type of personality and somebody argues a 3D image will make something seem more tangible (whether that’s true or not), then if you take that too literally, that’s really going to hit your hot buttons.

Normal people are not so literal though. In fact, I think few if any people are ever so literal. Box shots and ebook covers are just graphics, just like any other. People know that. It’s the same issue that nobody complains where is the paint brushes or calculator in Windows, because there are icons with pictures of them. Nobody complains about the icons in a million online stores (say Music stores) to select a download, are graphics icons, and you don’t get a CD or a physical poster.

Of course, if you’re evil enough, it’s probably possible to come up with box and cover uses that might be deliberately deceptive – and you should obviously avoid these. Likewise it’s probably to come up with some box/cover uses that might be accidentally deceptive – so if there is an possibility of doubt or confusion, it doesn’t hurt to add a brief notice to your site clearly explaining that box/covers do not represent physical products, and the product is delivered by download only.

And finally let’s not forget that boxes and covers are not just for sales web pages. I’ve seen them used very effectively in other manners, such in software splash screens, the first page on an ebook/help file, and all sorts of other things.