Well, seeing how the "rules" about shooting at multiple stories were more like five pictures with small accompanying text, and they seem to be missing in this edition, I sadly have a real hard time to think that it's just a mistake. I do hope it is and they fix it.
However, if intended, it is a horribly dumb change and in our local game store we're doing things the old way. I simply refuse to try to come up with interpretations for situations where an important clarifying rule is left out completely. Why would the impact of a blast weapon grow with the amount of people in the ruin? Likewise, how exactly is one supposed to shoot with flamer templates on elevated positions if we are to hold the narrow end of the template to the base of the model that shoots it?
There are so many inconsistent or dubious rulings in the new edition that have replaced the old ones that they make my head spin. Playing the game competitively almost requires one to posess a degree in Law or have a lawyer by their side to decipher the rules.