I've read many posts re negotiating the relationship/start-up gig. This article presents one solution; do it together.
But this is probably not the best solution. It's extremely difficult to draw a clear line between work and relationship especially when both of you are spending 90% of your waking hours on the same project. A problem with one side will very likely lead to a bigger problem with the other....
It would be interesting to gather some data about it. Offhand, what you say seems right - I don't think I'd want to work with my wife. Who knows, though.
Now if they would only do a piece on how unsuccessful startups ruin relationships and destroy marriages...