Loyalty is what we call it when someone refuses a momentarily better option.
If your offering is always better, you don't have loyal customers, you have smart ones. Don't brag about how loyal your customers are when you're the cheapest or you have clearly dominated some key element of what the market demands. That's not loyalty. That's something else.
Loyal customers understand that there's almost always something better out there, but they're not so interested in looking.
Loyalty can be rewarded, but loyalty usually comes from within, from a story we like to tell ourselves. We're loyal to sports teams and products (and yes, to people) because being loyal makes us happy. Why else be a fan of the Cubs? Some customers like being loyal. Those are good customers to have.
Loyalty isn't forever. Sometimes, the world changes significantly and even though the loyal partner/customer likes that label, it gets so difficult to stick that he switches.
I think there's no doubt that some brands and teams and politicians and yes, people, attract a greater percentage of loyal fans than others. Not because they're bigger or better, but because they reinforce the good feeling some people get when they're being loyal. Hint: low price or supermodel good looks are not the tools of choice for attracting people who enjoy being loyal.
Rewarding loyalty for loyalty's sake--not by paying people for sticking it out so the offering ends up being more attractive--is not an obvious path, but it's a worthwhile one. Tell a story that appeals to loyalists. Treat different customers differently, and reserve your highest level of respect for those that stand by you.