I get missing ports is a part of cruising. I was on a European cruise last year and we missed 2 ports due to weather. The cruise line was very apologetic and not only refunded the port fees and taxes, but also provided passengers with refundable credit.
Advertising a cruise and then pulling a port for no good reason (I have never thought to myself 'gee I need more sea days') is poor customer service. Refunding $11 seems like they are thumbing their nose. If they want to change next year's itinerary, fine, but don't change it when many people have already booked.
I won't let it ruin my cruise but that doesn't mean I can't complain about it.