The $10 gratuity your friend refers to is the blanket gratuity that is charged on a per day basis per guest in each stateroom, but it is not specifcially for room service. It is the total of the requested per diem rate (per guest) for your stateroom attendant, dining room waiter, assistant waiter and head waiter. I usually tip the room service attendant $1 or $2 depending on the size of the order - but it is not mandatory. Also, unless RC has changed their policy within the last couple of weeks the actual per guest rate is $9.75 and according to RC is handled in the following ways:
Envelopes for gratuities will be provided in your stateroom on the last night of the cruise. Gratuities may be paid in the following ways:
Pre paid by having them added to your reservation by your booking agent.
Added to your onboard SeaPass account.
Paid in cash at the end of the cruise