I've never seen this before, and I've read the passage plenty of times. I always thought (until now) that it sounded as though James was just chiming in with his opinion, after which the whole bunch decided (perhaps by general consensus or perhaps by a vote) to take his advice. But when looking up the Greek word κρίνω I found that it can carry the connotation of a decree or decision (sometimes a judicial one), and Zodhiates applies this connotation to the use of the word in Acts 15:19 specifically. The language of verse 28 can be seen to support this understanding. It looks to me like they really intended to make a more-or-less official pronouncement in their letters after all. And James, brother of Jesus, was quite clearly more "in charge" than either Peter or Paul. The others deferred to him. It's as if he sat as a presiding judge, listening to the evidence and then making a ruling.