Even shares on "gross profit" can fail: it can be beneficial for the publisher to give away the product for free. I've had this happen to a J2ME app, which the publisher gave away for free in exchange for advertising (they were building presence and reputation by this).
Another trick seems to be bundling - "buy this collection of things and you get thing x for free". So profits for selling thing x would be zero.
Another trick seems to be bundling - "buy this collection of things and you get thing x for free". So profits for selling thing x would be zero.
I am sure there are many more tricks like this...