United Airlines has changed its MileagePlus loyalty program to eliminate the provision that expired miles if there was no account activity within 18 months. The change takes place immediately, and follows Delta's decision in 2011.
Other programs, including American and Southwest still have expiration points, but like United's those plans allow keeping the miles alive by many means including earning more with a co-branded card, shopping on the airline's shopping portal, or even by spending some.
Loyalty programs are a big cash source for airlines; they sell the miles in bulk to credit card partners, stores and others who award them to program members. That's a direct cost to the partners, but none to the airline until and unless they are redeemed. Expiring the miles allows the airline to keep what it received and not have to pay out in award tickets for the expired miles.
In another, smaller, consumer-friendly move, United has also added the ability to pay those consumer-unfriendly bag fees online anytime between buying the ticket and showing up at the airport, potentially saving a line at check-in.