I agree with the article - you can succeed without a co-founder, and yes, I think it's true for software start-ups as well. In fact, ShutterStock is a web service (kind of a software start-up) founded by one guy, as far as I know, who is now a billionaire. I'm in the software business myself, and although I have a junior co-founder, I don't really need him - I can do all the work myself.
A co-founder is really needed for two reasons:
a) Psychological support: entrepreneurship gets REALLY lonely sometimes, if no one shares your vision.
b) Statistics says that lone founders fail more often, so most investors simply won't invest in a lone founder (unless the startup is already successful).
If you can handle the loneliness, and you have the necessary technical skills to do most of the work yourself or have enough money to hire freelancers (although for this you have to know how to manage them properly), then you don't really need a co-founder.