I'm sorry your cruise didn't go exactly as planned, but that is just the nature of cruising, in fact, of travel in general. Wind and bad weather don't abate for the top cruise lines--it can affect any line, any ship.
To answer your questions:
1. I won't say it happens frequently; but you have to keep in mine that the safety of the passengers and crew is of paramount importance. You didn't say if you were going to dock or tender in. Skipping a port because it is to windy or the seas to rough to tender safely is rather common. And there have been several incidents just recently of cruise ships sustaining damage while trying to dock or leave port in high winds.
2. Yes, there is a tinge of sarcasm in the statement as quoted; but that dosen't change the truth of the matter: NOBODY can gurantee the weather. Personally, it dosen't offend me at all.
3.Yes, that is true. How to you know that the Captain didn't make every effort to arrange a stop at another port? My guess is that he probably did just that. You have to understand the myriad cirsumstances and decisions that go into makeing a last minute port substitution like that. Time, distance, weather, customs, local laws, port traffic, all must be taken into account. A cruise ship can't just show up and say, "you got a spot for us?" (and yes, there was more than a little sarcasm in that statement :-))
Silversea IS top of the line, and even though it may not have felt like top of the line service, I'm pretty sure it was.