Claudia, they are not. They are independently owned. The one advantage though that Kristen mentioned, is that if you do go on one that is a Venetian Club discounted sailing and you join someone on that sailing, you still get the discount. Also, SS discounts the 5% or 10% off of the full fare, not the discounted fare. A really nice perk! AMEX Platinum is similar to RSSC. It is a $300 shipboard credit and a bottle of Dom Perignon.

Oh, one other thing. You can have someone else that is sailing on SS book the cabin for you when they are onboard and you would still get the onboard booking discount even though you haven't sailed on them yet. That particular cruise is only a 2% booking discount, but again off the full fare. BTW, I leave in April. ;)