To me, they do carry different meanings, but very slight, and the difference may not be intended by the writer.
"Developments" can mean both "evolution" or "growth". The evolution of something can either be for the better or worse or just different, whereas "growth" is always positive.
"Developments in", to me, indicates "evolution". For example, the stock markets are focused on the changes of US-China trade relations whether for the good or bad - they just want to know.
"Developments of" is strictly positive: the stock markets are focused on the progress being made in the US-China trade relations.
"In" could have been chosen here because they are genuinely interested in any changes (because if things go bad, people may want to sell their stocks), but then the second phrase makes it clear that they are particularly interested in positive changes.