Methinks the OP (and others) should be happy they got to their destination that night at all in any case. I faced a similar "plane swap" situation in FNT a few years ago, back when XJ was flying Avros. We were waiting at Gate 1 DTW-bound when the Gate 2 MSP-bound flight went MX. Ops swapped gates and we found out when all the MSP pax marched into the boarding area; looking up at the monitor I could see that it now read MSP with their flight monitor. When I walked over to 2, our flight was listed as CX.

Since these were the last flights of the day, I hustled down to the counter, only to be told it would be a couple of days until NW could get me to WAS (high loads). I ended up staying home that week after declaring "trip in vain" and getting a full refund on a "non-refundable" Y fare. The work suffered a slight bit, but I didn't feel it good stewardship of the Company's money to fly down there for only a day's work (Thu).

So, again, be glad everyone made it that day.