50/50 Cofounders
avc.com
avc.com
I think it was Joel Spolsky who explained that point of view best some time ago.
Beyond his explanations, though, the non-tech world has lots of "silent partners," people who may own half or more of the company but give up the actual power of running it. Ideally, you give up some ego, power, and responsibility without giving up freedom and financials.
Friendship based on fairness typically consists of mutual respect and confidence in each others capabilities and shortcomings. Such friends have most certainly learned to appreciate their diversity and face another on an equal footing. In this case, a uniform split would be a natural fit - anything else would question the fairness of the relationship.
The problem I see is that even in long-time friendships it is not always clear what type of relationship it is. I would claim that in every relationship, all aspects (fairness, personal benefit and more) are present to some amount. And as you say yourself, each member could understand the character of their friendship differently.
The implication is: Before deciding how to split, find out in what kind of relationship you are. A russian proverb comes to mind: If you want to get to know someone, go on a mountain hike with him. My russian-speaking friend told me that one, and in fact, we went to the mountains together. Almost died several times. We know each other very well now :)
If the contribution was wildly different, I think that's certainly a different case.