(I'm behind both)
To me, first and foremost, the fact that you don't have any out of pocket expenses is a good thing, it eliminates one barrier to entry. Virtual companies achieve that. In comparison, joining a "real" incorporated startup as co-founder, the first thing you do is split the legal costs and buy your shares. So right there, a few thousand dollars before you even know if you should work together. And there is no "undo" button, unlike virtual companies.
That's also why in the co-founders meetup I ask the presenters to not only present their business, but reveal a bit of their own personality. I believe that compatibility as co-founders comes equally from being passionate about the same things but also being compatible personality-wise (read this http://blog.fairsoftware.net/2009/11/19/first-co-founders-me... for more on the topic).
This is true only of American dating sites. A number of Indian dating sites are based on that exact model.
I guess the lesson to take from that is this: if your expectations are low enough, and social pressures not to quit are strong enough, any reasonable pairing can be made to work.