xcode - iOS Universal app / separated apps. Development considerations -

i know there lots of posts dealing issue, i'd want make clear points concerning development effort rather pros , cons users. i've read in several threads (a recent example: developing ipad / iphone application in same project or in 2 separate (monotouch)?) developing universal app "worse" developer's point of view, , don't entirely understand why:

1. is better have duplicated code business logic having lot of if statements different iphone/ipad paths?
2. even if have separated projects iphone , ipad, you'll need design appropiate nibs/storyboards, having 2 versions each nib/storyboard in same project problem?

maybe i'm misunderstanding how separated iphone , ipad apps developed: i'm thinking separated xcode projects. possible create target each device within same project , implement common stuff once?

thanks in advance