I can agree with you about HRE abuse maybe, but the ship one is clearly a bug. It's implemented the way it is because actually remembering the price of each ship when it was bought is extra work and they didn't anticipate it being an issue, just like making a popup block the screen is extra work/annoying and they didn't anticipate it being an issue. Making ships sell for more than their cost is not a result of being creative with the rules the game gives you, it's a case of abusing the specific implementation of those rules in the same vein as the popup bug.