Right, but you can argue ranking N items takes more thought thank picking 1. I like the "interoperable" way, just making choices 2 and onward optional.
Given the wording in the article I'm almost certain that underfilling the selection wouldn't result in a spoiled ballot. People can continue to just pick their favorite dude and go one with their lives. From a survey mentioned in the article apparently only a quarter of potential voters choose to only make a single choice[1].