I love how precise and detailed this article is written. If only more documentation were like this. It was always my assumption that grammar is the most important thing to learn about a language. Vocabulary accumulates almost automatically over time, with practise (and a dictionary). Interesting to see how that holds in this case.
I think it depends on what your goals are. If you just want to communicate, vocabulary is the most important thing to get started, since even with poor grammar people can infer what you mean (gestures help too!). I've seen too many people here in Japan who have crammed English grammar all their school years but are paralyzed when trying to communicate because they're just focused on getting the grammar right.