When things that act as levers are attached to aluminum, even small forces can crack, break, or tear the aluminum rather easily. Besides broken aluminum levers, I have seen minor parking lot tip overs result in cracked or broken thick aluminum footpeg mounts, snapped aluminum rear subframes, broken aluminum mounting tabs from main frame spars, snapped off shock mounts, etc.
While not a common occurrence, there have been cases of bikes tipping over on an off camber surface and rolling past the point of just resting on the pegs, tip over bars, or side cases. Depending on the mounting position of the tank and the filler location, such a situation could result in the filler neck hitting something solid with the momentum of the bike behind it. That could be enough leverage to tear the filler tube out of the side of the tank (the welds might hold, but they are stronger than the thin sheet the tube is welded to), resulting in a spill. A similar situation could occur during a crash, with similar results...unless the bike is sliding and creating sparks, which might be a bit more serious.
The ease of bending or breaking aluminum is one of the reasons I like to use it for aux light mounts instead of steel. It is light and strong enough to hold the lights securely, but in case of impact the aluminum is likely to fail before transferring a lot of force into the more expensive and harder to repair subframe of the bike.
When you look at some of the things that have happened to rally riders over the years to put a damper on the rather extreme amount of time and hard earned money that riders put into getting themselves to the starting line of the IBR, it seems reasonable to me to do as much as possible to set up a rally bike to survive a parking lot tipover or gravel road bonus crash or even a lowside in the rain. Picking the bike up, finding only minor damage, and continuing the rally sure beats seeing a couple of years of prep going down the drain....or up in smoke.