This is an interesting perspective, and something I am trying to consider in my equation. I agree that the contribution each co-founder brings to the table should be based on the overall value, regardless of the hours he spent to achieve it. For instance, if one of the co-founders is able to land a big client or investor with a couple of phone calls then I certainly wouldn't worry that I am working 90 hours/week developing the product.

One problem remains: finding people who can close big clients or investors over a couple of phone calls is pretty hard. Identifying them upfront might be even harder!