hold on, lets define some terms here.
demo in my line of work is a preview/beta. I referred to it as a demo - very confusing on my part. a true demo, which we get on a cover disk should work, as you say.
we release beta's with known issues and bugs because all the business care about is the useablility, they know that problems will be fixed.
for a preview to a magazine i would say that this is the same. its not an official demo, as we would think of it, on the front of a magazine/available for download, but a version that gives them the gist of what the apps all about.
i guess my long winded point is that the preview copy is a beta, and i would imagine chock full of problems but the core game still works.