The rule Squeaker speaks of is accurate a fair amount of the time, but their are some exceptions. Some fish, such as your Puffer, have a lot of girth to them in addition to their length, and therefore need more space. Some fish, such as your Jack, simply get to big to follow that rule (adult size for a Jack is 10 inches, would you honestly ever keep a 10 inch fish in a 10 gallon tank?). The final exception is that some fish, such as both your Jack and your Puffer, are highly territorial and therefore need more space simply to keep from bickering with each other. With your current stock, you could do quite well in a 55 if you divide up the tank into territories using plants and rocks and make a lot of caves for the Jack to claim. I wouldn't add anything else though.

Oh, and to answer your final question, the reason you see all these crowded tanks online is because a whole lot of people are dumb and don't follow the rule Squeaker mentioned earlier, or follow it but don't take into account the adult size of the fish :P

marcus, you should start a new thread for this question. Click on freshwater forum then click "post new topic". It's not a stupid question at all, but you will get better feedback by starting a new thread.