Nope. It's this way for refineries because they only have a range of 1 jump, and each resource extractor can only support 3 refinery ships (each refinery structure makes 1 ship for each mine in range).
Trade ports have no jump limitation and no upper cap, and get a bonus to their output along the longest uninterrupted chain. So basically, feel free to put them everywhere and you'll keep getting more and more money.