Is not a better pull rate, sets are splitted, if you know the content, you can preset what you are gonna obtain, lets say I want to pull a non art reshiram or an emboar with ability, I only need to buy Black collection packs, since they are only included in that set, I buy 15, I get both and also a secret pikachu, but is imposible for me to get Zekrom, Zoroark, Reuniclus, Thundurus, Samurott with ability or any other stuff exclusive to the white collection boosters.
Boosters in japan have fewer cards, but the carlist is smaller as well; in america we have a differnt rarity setting, we get 10 cards per pack and a "chance" to obtain 2 rares with a bigger cardpool, making harder to get what you WANT, but in the end the good stuff pull rate is the same.
Also, we have some advantages over japan, specially when it comes to promos, remember japanese raichu prime got up to 500 bucks on auctions, Espeon and Umbreon got even harder to obtain; you needed to win like 3 tournaments in a row to earn them, we on the other side of the ocean just need to buy undaunted packs and complain for not getting a scissor instead of those crappy primes.