Not everyone wants to rip off the government or save money. Some people just want to have the security of knowing where the fuel is in times of stress in our economy. The last time that happened with gasoline, was about 1979. There was also rationing in 1973. That is twice in my lifetime. Gas was rationed in the 1940's as well. So, it is a once in 25-35 year occurance.
A lot of people feel that we're heading for another crisis soon. Those who poo-poo the idea might want to read up on the term "peak oil", or take Chris Martenson's "Crash Course" at http://www.peakprosperity.com/crashcourse
. While I am not entirely in agreement with everything Chris says, I think it is a great start to understanding our economic world.
The bottom line is that if we are approaching some sort of crisis, having a small supply of fuel might be a good thing. It wouldn't last long, and it probably wouldn't be worth the investment, but some people are sold on the concept that we might enter a world more akin to that of Mad Max than what we've experienced in the past.
I will offer that during the crises in the 1970's, the singer John Denver kept a private fuel supply on his property in Colorado, and his neighbors were acutely aware of it and didn't approve.
Enough said on the topic. If you are producing your own biodiesel or ethanol, having such a storage tank might be warranted, but as mentioned in the other responses, fuel goes bad faster than one might think, and there isn't much economic incentive to do this.