Agreed, that's absolutely important, but life gets in the way. Things change, priorities change, and opportunities change. The dynamic split helps those who contributed early keep a stake even if they need to make a change later. It also gives an easy way to reward those who step in to contribute later. And this is done without absent partners potentially strangling equity from other contributors.
On finding a business partner: do some sort of tangible work with them before you start on a larger project, make sure you've got some seriously deep social validation of them and be sure you have a complimentary skill set. Oh, and liking them helps.
My business partner and I were able to spend all our time arguing about the product rather than whose contribution was bigger.
I agree with @hmurakami on this: http://news.ycombinator.com/item?id=4940379