Yes, I heard the same thing; St Lucia isn't the favorite spot for some. I have noticed Celebrity does seem to change itineraries more often than some lines. For me, it usually isn't a big deal, cruising is cruising, for some the ports are why they book a particular cruise. Of course we too look at the ports before deciding but it isn't our number 1 determining factor.
The Connie is one ship that changed the itinerary about 2 or 3 times last year. Actually all lines do this some for various reasons; None of us know for sure the reasons. Last year for a short time they dropped St Martin and picked up Casa De Campo, then went back to St Martin. In January St. Lucia was dropped for Grenada I believe and Casa De Campo picked up again. At least I think I have this straight, but am not sure. AS I said this does happen, usually not at the last minute though. As for notifying everyone that has booked, no they do not. They do let TAs know. If you are using one he/she should let you know. Don't let this bother you as it doesn't happen that often. Just relax, enjoy your cruise and enjoy the ports regardless of which you visit. The only time it is a problem to us is in the event we have seen the island several times and had planned on another. Even then, it isn't worth worrying about.
Guess Constellation does change itins alot. We are booked for 9/20 Canada & new Eng 10 day & have just heard we lost our only port in maine--Now there is another sea day. Unfortunately we wanted that ship & that week & the other choices are either a much larger ship on Royal, going later when it will be colder or leaving from either Boston or Baltimore. I guess we will stick to it but wonder what we will do on these sea days when we are not in a warm climate? The aquaspa won't accomodate everyone--Guess there will be bingo etc. Still looking forward t oit but it was a bit disapointing.