No one should be shocked by this. Today's LCCs are not what they were just a few years ago. New planes, full-sized jets (as opposed to turboprops on too many routes), in flight entertainment in the case of JetBlue and Frontier, simple fare structures that are understandable and don't gouge the last-minute traveler. Of course this was going to happen.
There was a time when the legacy carriers offered more in-flight ammenities than their el cheapo competition. I just don't see where that's the case any longer. Personally, I remain a pretty loyal US FF, but for flights between NYC and upstate New York, I choose JetBlue just as often as US these days. Those Dash-8s just aren't that appealing - especially in the winter months.
I stick with US because of a very good FF program - dedicated reservations & customer service lines for preferred passengers, frequent upgrades to first class, priority check-in and boarding. The Shuttle and US Airways Clubs are also a plus for me. These benefits still set US and other legacy carriers apart from the LCCs for frequent fliers, but there are only so many of us to go around. For people who fly on business once or twice a year and take their family on a vacation or two, what's the upside? How would you convince them to choose a legacy carrier over the new LCC with the new jets, leather seats, extra legroom and those cute little TVs?