Making The iPhone Before The iPad

Steve Jobs had mentioned in an AllThingsD interview that Apple had started working on the iPad first. Then they decided to make a phone based on the same technology.

Just curious, based on the variables during that time, why would they have decided to work on the iPhone first?
Better still - why did they not work on both at the same time?

LinkedIn CEO recently pointed out that this could have been due to focus - but could there be other reasons?