Looking at Acts 16:4 in context, it had nothing to do with just any ol' decrees that came out of Jerusalem. This is right on the heels of the main issue of why Paul went up to Jerusalem to begin with.
"I went up as a result of a revelation, and I presented to them the good news that I am preaching among the nations." - Gal 2:2
The false brothers came down from Judea, of which Jerusalem was the capitol city. The "decrees" were that the Gentiles did NOT have to get circumcised, and "to keep abstaining from things sacrificed to idols, from blood, from what is strangled, and from sexual immorality." (Acts 15:29).
This is the ONLY place in the NT that talks about decrees being followed. Thus, is was a VERY PARTICULAR set of decrees related very much to the issue false brothers were pushing onto the Gentiles.