Yes, on Crystal tipping is expected at the end of the cruise.
However, if you have "prepaid gratuities" from your TA, you are given a statement at the beginning of the cruise which states the amount of the tip to each service provider which will be paid on your behalf ( stewardess, waiter and ass't waiter) About 2 nights before the end of the cruise you are given individual "chits" or cards which state the amount of tips to each service provider and envelopes to place them in.
In essence, these chits are the same as cash that you would give to each. In addition, the chit has your name and cabin number.
On our last Crystal cruise from Buenos Aires to Miami, the service and food was extraordinary so we added cash to the prepaid chits for everyone.
The amount of the prepaid gratuity is the amount that the cruise line recommends that the cruiser tip to each service provider.
We also cruise on Regent and do not tip extra for room service or dining room service. We will tip extra for "extraordinary" service. My wife does tip "extra" at the hair salon and spa.
We are scheduled for our first Oceania cruise next March and, unfortunately, we do not have prepaid gratuities from our TA. (We should've booked with Ngaire, her TA provided prepaid grats) We have a PH and tipping can add up quickly. We do not intend to tip the butler for each room service order delivered but will tip him and all other service persons at the end of the cruise. Hope that is the correct procedure for Oceania.