Actually, that vanilla smell in the rubber is not the extract of vanilla. That is artificial vanilla fragrance oil-ethanol based. 1litre of the good grade real vanilla essential oil is about USD5k now, more expensive than some Swiss watches.
All natural rubber will add this artificial vanilla fragrance oil to get rid of the natural rubber nasty rotten smell (if you tapping rubber tree before you will know that nasty smell), in fact all tyres got this vanilla smell too.
But for synthetic rubber because it is not natural rubber base, it wouldn't have the natural rubber nasty smell so no vanilla fragrance oil needed.
Hope the above clear the doubts. But its eye-opening experience how the AD salesman really know how to "talk" anything to market their watch.