The way I understood Spolsky the IOU was between the founders, i.e. it would even apply if the company went bankrupt. If that is the correct interpretation, they share the same risk.
I re-read the entry and it isn't clear to me if Spolsky thinks the IOU should be there even if the company ceases to exists. Me and my two co-founders had a similiar arrangement, albeit with very small amounts, and after the company died they paid me back the unofficial loan. We were all students and I happened to have some more disposable money for initial investments (under $3000 though).
I re-read the entry and it isn't clear to me if Spolsky thinks the IOU should be there even if the company ceases to exists. Me and my two co-founders had a similiar arrangement, albeit with very small amounts, and after the company died they paid me back the unofficial loan. We were all students and I happened to have some more disposable money for initial investments (under $3000 though).