Staggering, simply staggering. Its now so much that I think I'm right, its more a function of that I know I am right. The ground plug (even though it goes to the same place in the panel) PREVENTS YOU FROM SHOCKING YOURSELF. Nothing more, nothing less. NO, the absence of this plug doesn't increase the risk of fire but it does provide the opportunity for you to electrocute yourself. If you have an appliance with a metal case, and the appliance somehow shorts out, it will not flip the circuit breaker and shut off power to the device without a proper ground circuit. Electricity will keep flowing through the object and its case in so much as if you touched the metal case, now the electricity would be flowing through you.
The little metal tang on an adapter plug isn't "so it doesn't fall out" its to provide some measure of a ground. (although not as good as a true ground) . The simple fact that you think its there to hold the adapter in place seems to underscore the fact that your none to wise in terms of how electricity works in a residential application. Find me ONE SINGLE reference that says its advisable to use a 3-2 prong adapter over a true ground.
I even went as far as installing an AFCI breaker in the supply that feeds my grow room. Necessary? (well by current code yes) but by "will it work without it" standards. No. But if I develop an arc fault in my room (I dunno, say bulb shatters in the night) or I drove a nail into the wiring in the wall and didn't know it. At least I won't burn my entire house down, killing my family with it. Believe me, I take MANY a calculated risks in the name of fun but if there is a simply, cheap and effective method to increase your measure of safety, why on earth wouldn't you take it? Seriously?