The detailed PEGI 16 - Drug and In Game Purchase rating are described in the official PEGI.org website.
Runescape:
Content specific issues
The player's character can gather resources in order to brew their own alcoholic drinks. The consumption of these drinks gives health and status benefits.
Other issues
This game offers players the opportunity to purchase in-game items, in the form of coins, bonds and treasure keys, which can then be used to obtain cosmetic items and other benefits. The treasure keys can be used to unlock treasure chests, which contain random items. Some parents or carers may want to be aware of this. Parents, carers or other responsible adults should check to see what is being offered before making any purchase on behalf of a child. It should be noted that the game can still be played without the need to purchase such items.
OSRS
Content specific issues
The player's character can gather resources in order to brew and consume alcoholic drinks. The drinking of alcohol gives health and status benefits.
Other issues:
This game offers players the opportunity to purchase in-game items, in the form of Coins, Old School Bonds and memberships, which some parents or carers may want to be aware of. Parents, carers or other responsible adults should check to see what is being offered before making any purchase on behalf of a child. It should be noted that the game can still be played without the need to purchase such items.
I believe Jagex can't "get it off' as that label and descriptions may be required by regulations of some countries. Basically some countries require Jagex to disclose RS3 and OSRS and whatever new games have pixeled drugs and MTX.