I wouldn't be surprised if this was a pre-watershed advert.
I was about ten years old when I was over 140cm...a lot of the darker sides to say, Oblivion went over my head but I was still able to ride the coaster and enjoy the coaster. There is still a family market with this ride. It won't appeal to families with kids of 9-12 years old if the ride is marketed at 18+. I hate to burst everyone's bubble in thinking it's a coaster only for adults, but it simply isn't. Furthermore Alton Towers, unlike Thorpe Park, directs its marketing at everyone. An advert shown before 9pm has to be appealing to everyone. Even if the family has small children and no one has any intention of going on the Smiler, if you show the park as being a terrifying, thrill-seeking place these families won't want to go and ride the significant portion of the park that is suitable for them and does actually provide them with a good day out.
If I am correct, there'll be a post-watershed advert. Whether or not it will be like Th13teen whereby it was the same advert just with a little more 'dark' bits, or genuinely a whole new advert (Which I'm hoping for...there's so much potential!) It's hard to second guess the marketing department...but we can hope!
I'm just praying that the cynical side of me, that says the marketing has changed because they feel they 'over-darkened' Th13teen so therefore they don't want to go down that route again...hmm...