That's not always the case. For example, I've seen a couple threads and spoke with people in game about the castle suite guest room. It is listed at a "max" of 20 walls. (20x40k=800k) People trading an item of this rarity typically ask for more credits. 1 million credits seems to be the settled value for this particular item. The furniture also goes for about 100k each, only 10k off from the "Max value" in firewalls.
Also, the firewall value fluctuates while credit values tend to stay the same.