Remember that weather at the city of origin of the [b]aircraft[b] may cause your delay or cancellation. For instance, a month or so ago, my flight MSP-EWR was delayed 5 hours because of weather in DEN, where the aircraft originated.

Now, I'm not saying that this happened in your case. It could have been any number of things. Often, the gate agents don't receive very good information. They may be told it is a weather cancellation, even if the real reason is something else. One possiblity is that delta decided to use your aircraft on a different flight (to replace a plane with, perhaps mechanical difficulties). This is probably done when the other flight has far more passengers and/or it is much more difficult to reacommodate those passengers than the ones on your flight (such as the other flight being the last one that day, while your route has more flights). Some of us do suspect that airlines will occaisionally cancel planes for economic reasons. I think this is likely very rare, however, economic decisions do likely factor into the decision to cancel a flight to use the aircraft on a different flight.