All airlines do this. I've had WN planes swapped because downstream wx or maintenance throw a wrench into the operations. QX cancels because of weather all the time. They just cancelled an early August SEA-PDX flight I was on for a late inbound aircraft.

Think about it: if you have to inconvenience passengers, is it better to inconvenience 70 or 150? Not to mention the downstream pax who might be inconvenienced.

The difference between WN and a lot of other airlines: WN will usually opt to delay flights over canceling them, even when doing an aircraft swap. Your flight might land at 4am, but it'll usually operate.

My delayed AS119 will be getting in at 2:43 AM it seems right now :o

Apparently the lav was signaling as full, despite being emptied. Yes... we were full of... :o

Just went through stuff at DFW on pmAA tonight. My flight had six different gate numbers today, five after I arrived inbound to wait for it. It also had four or five tail numbers assigned by the time it was all over. We ended up just under an hour late, though predictions at one point were worse. Kudos to the gate crew for doing a fast turnaround on the 321. Who knows why they swapped aircraft assignments, but I suspect that one reason was to send a plane back to PHX for people with evening connections, where my flight into SFO would have very few, if any, and the plane was parking overnight. Maybe they were pulling monkey business with their stats, but I suspect it was for more legitimate concerns.

When they have to cancel a flight they will cancel the one with the least downline effects. Many times that's the lightest flight but not always. Have to remember the plane and crew may be used on several flights on the same day. So the light flight may go because they have a full flight down the line.