I don't think you are reading this correctly. Are you taking into consideration the fact it is ONLY comparing MAXIMUM BTU OUTPUT? The chart is not saying "a Progress puts out 3 times as much heat as a 30". It is saying, with a full load of EPA test wood, the MAXIMUM heat each unit will put out is xxx btu's. That does not mean it can do it for very long, or very short, or any lenght of time for that matter. Just that it can do it.
Here's an experiment for you to try someday. Load all three of your stoves with the same amount of the same type wood. Say, two 4 lb splits of oak for examle in each stove. Light them up, and leave them full blast open. Now measure (as best you can), how much heat each seems to put out, and how long it takes each one to burn down to the same point (10 or 20% left in coals). THAT, is what I believe they are showing you in the graph. (EDIT: All three will very likely product completely different results, different outputs spread over different time period, with different peak outputs, and different low outputs.)
Does it show you exactly what a stove will do in your home? of course not. Nobody is saying that. It is a reference point.