swamt,
publicly traded companies have to provide reasonably accurate guidance to investors and the SEC regarding any item that can affect their earnings and stock price.
They can't hold onto information that would indicate strong earnings just so they can amaze the market and watch their stock price rise.
They are also required to inform the market if they will miss expected earnings - UAL has done that several times since their merger.
Finally, no airline stock has "plunged" including DL, esp. if you look at the stock price over more than just a day - but even UAL has seen several days of late than have involved 10% drops in stock price only to recover much of that in the following days.
Recent weakness in the airline sector's stock prices have been driven by higher fuel prices - which are coming back down - and more significantly by concern that capacity discipline is going out the window in favor of market share gains which is what has happened many times in the past to the detriment of airline earnings.
Lufthansa mentioned it first then DL echoed those comments. It is likely valid given that UA has cut several TATL routes on either a seasonal or permanent basis. LH is also reducing its capacity to JFK during the winter to a little over one flight/day to FRA. For one of the Euro megacarriers on one of the largest TATL routes, that is not a lot of capacity.
DL also said there is weakness in Latin America which appears to be related to the Cup but if a significant amount of new capacity in Latin America such as with WN's new service starts to depress yields or results in other carrier capacity additions to balance what WN is adding, then the problem could be longer term and indicate that the problems of overcapacity could undo a strong market in Latin America right now.
The domestic market is strong which is good for WN particularly but given that WN has a lot of new markets to develop over the next six months plus has focused their growth on int'l markets, what is happening outside of the US will be more and more important to WN.