Most the time when airlines quietly change a rule, it means they're trying to slip in some kind of unwelcome change under the radar. But there's another type of hushed rule change: the kind when the changed rule benefits passengers. However, airlines typically don't want too many people to know about it because it, you know, benefits the traveler.
I have a strong hunch that the recent relaxation of the rules around the post-booking grace period fall into that second category. According to the London-based Times Online, some airlines have recently adopted a "24-hour rule that allows customers a cooling-off period to amend a booking without penalty, but little has been done to make customers aware of the new policies." Airlines with this policy currently in place include British Airways, Continental, Delta, KLM, Lufthansa, and United.
Bottom line here is that many travelers, even those who accidentally choose the wrong date or book a flight to Bucharest instead of Budapest (the example the article gives), don't know that there's this easy fix if you catch the mistake fast.
Because let's face it—booking mistakes happen. So it's nice to know that at least some airlines have a 24-hour rule to correct those errors.