At a few cents difference, especially when at most I'm pumping around 32L of gas now in either of our Volts, I won't bother.
But at 20c difference, yeah, I'll lineup at Costco for the 10 minutes it might take to get a pump - even on 30L of gas that's $6 saved.
The problem is, most people are blissfully clueless about how much gas their car even uses - ask the average driver their L/100KM and many will give you a blank stare. Many couldn't even tell you how many KM they can get on a tank - they just drive until it's on E, and pump. They don't even understand that driving 25KM return (out of their way to a Costco, for example) on a car that burns 10L/100KM is costing them $3.25 in gas at todays prices. If they're pumping 50L and saving even 10C/L versus a closer gas station, they're only saving $5, for a net savings of a mere $1.75.
A smaller tank, or a longer distance, and that "saving" can be wiped to nearly zero...or a loss.
But again, some car drivers can't even open their own hood, much less calculate this sort of stuff.