That seems like an insane assumption to me. Maybe there’s nobody worth voting for. If you don’t interpret a non-vote that way what’s the point of democracy?
I wish people would probe this question a little more. It certainly seems to me, what with the party-based system (and all their rules, requirements, and other methods of disincentivizing non Republican/Democrat participation), the point is not democracy at all, but political power brokering. That's not a system I'm comfortable interacting with.