It's more that I'd like to demonstrate that there are exceptions -- and so far I can't think of a single instance where having a cofounder would have helped me.
I don't see two as a natural lower bound on the number of founders. As the productivity of individual programmers continues to rise, I expect to see an increasing number of single-founder startups succeed.
You need a sounding board and a source of moral support absolutely. This is best done by a co-founder. However, it CAN also be done by someone who is not a co-founder and more of an advisor.
Also, you do NOT absolutely need co-founders with complimentary skills. That is a myth. Larry and Segie did not have complimentary skills. Bill Gates and Paul Allen did NOT have ALL the skills required to build their business. They had or developed (read learned) a lot of skills on the way, for which they could not hire immidiately - which is the only thing that is required of a founding team.