If you’ve ever asked what the fuss over frequent-flier programs is about, then you know that the answer can be complicated.

Airlines love them because they’re worth billions of dollars in business. They also mean the world to many passengers, because at a time when airline amenities are evapo

rating faster than jet fuel spilled on a hot tarmac, perks such as upgrades and preferential treatment are just about the only things that make air travel tolerable.

So when two major airlines recently decided to upgrade their loyalty programs, they caught this skeptic’s attention.

Delta Air Lines has eliminated the expirations on its frequent-flier miles. And Southwest Airlines has completely revamped its legendary Rapid Rewards, adopting many of the features of competing incentive programs.

The old Rapid Rewards program offered flight credit based on every one-way flight as opposed to the length of the flight or the price of the ticket, and unused credits expired after 24 months. The losers under the new scheme — frequent customers who fly on shorter routes and pay less for their tickets — are incensed that they will be earning fewer free trips in the future.

David Kazarian, a frequent Southwest customer based in St. Petersburg, Fla., has a laundry list of grievances about Southwest’s new program, including new limits on mileage redemption, changes to the way mileage is earned and accompanying service reductions.

Nicole Madril, who works for an insurance company in Lawrence, Kan., sounds more upbeat about the Southwest changes. She likes the way the airline communicated its plans to customers and is happy that the airline has eliminated blackout dates for redeeming mileage credits. She’s also pleased that her old credits were transferred to the new program.

I asked Southwest’s senior director of marketing, Ryan Green, who oversees Rapid Rewards, about the issues. He acknowledged some glitches in implementing the new program but said that overhauling the rewards system would make it fairer, more competitive and more profitable.

He bristled at charges that Southwest was becoming just like every other carrier, pointing out several key features that distinguish the airline’s program. Among them: no blackout dates, no fees to redeem points for tickets or change reservations, and no arbitrary threshold for redeeming seats.

Why did Delta change its program? I asked Mike Henny, the general manager of Delta’s SkyMiles Medallion program. He said that it came down to one thing: The benefits of allowing miles to expire no longer outweighed the inconvenience to passengers.

“After discussions with our customers through surveys and focus groups, it was apparent that they view their miles as a form of currency,” he said. “The breakage of these miles was of minimal gain to Delta, but eliminating expiration was a big win for customers.”

In other words, Delta is hoping that its no-expiration rule will set it apart from the competition and drive more customers — and more dollars — its way.

Unexpected program changes like this give you an occasion to question your loyalty. Have you read your program member agreement lately? Do you realize that your airline can change the terms of its agreement anytime, for any reason, with no required notification? Did you know that under most program rules, your mileage and your elite status technically can be revoked at any time?

Scratch the surface of these recent changes, and it’s clear that they haven’t really been made because airlines want to reward you for your loyalty. They’ve been made because they want to be rewarded with your loyalty.

Maybe I’m just being a contrarian, but the way I see it, we’re really fortunate. I actually like the program changes to both Rapid Rewards and SkyMiles.

We may not be so lucky next time.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine. www.elliott.org or celliott@ngs.org.

© 2011 Christopher Elliott/Tribune Media Services, Inc.