IN RCCL's mind - a "Cat C" really isn't a suite. They consider suites "Cat B and above".
If you ask for a robe, they will provide one. Cat B and above cabins get daily treats delivered to their rooms but Cat C's don't get this.
Conceriage Service is also provided for "Cat B" and above and I believe "Diamond Crown and Anchor" members also have access to this. Because RCCL missprinted several brochures, they have been known to give Cat C cruisers keys to the Counceriage Lounge if you politely ask the right person. On our last cruise we had a Cat C and April was able to score a key with some smooth talking but otherwise it is not automatic.
On a positive note - the Cat C cabins are very nice. We had one on Radiance and the extra room was worth it! You will not be disappointed in the room.
You may want to look at CruiseCritic website - there are several discussions on this topic on that board.