Jasper, to get to another issue which may be at the heart of what's causing your frustration with this, there is one "final" issue to these additive all-in bets that makes them quite different from "normal" betting. This issue was actually the subject of one of the slides at the 2009 Rio Summit. Matt Savage had presented this slide based on a question that Bob Ciaffone had posed.
The situation is as follows: Player A bets 100. Player B raises to 200. Player C goes all in for total of 270. Player D goes all in for total of 350.
Now, Ciaffone posed two questions to the membership: 1: does Player D's action re-open the betting to player B? and 2: If so, what is the minimum re-raise that Player B would have to make?
To the first question, there's universal concurrence that the betting is re-opened to B. Simply because B had originally raised for 100 and when the betting comes back to him it's 150 more (350-200 = 150), so the action is clearly re-opened to B. The somewhat stickier question is what is his minimum re-raise? The answer to that is also 150. The main reason? Frankly because "that's the way it is".
The alternative would be to say that the min re-raise is still $100 because neither Player C or Player D increased the betting by more than $100. Consider this: Let's say that Player C had chips and just raised it $100 (to 300 total), and Player D had chips and raised it $100 more (to $400 total), then if A smooth called, it would be 200 to Player B (instead of 150 with the 2 all-ins) and the min-raise for Player B would be.... $100. So we have the anomaly that if all-in's aren't involved and it's $200 to Player B, the min raise is $100, but if all-ins are involved and it's $150 to Player B, the min raise is $150. So this is an added twist to the whole story. I had e-mail correspondence w/ Bob Ciaffone on this illustration after the Summit, and despite the apparent anomaly from one point of view we both agreed that this arrangement is so widely deployed in the poker world that to try to change it would not be worth the confusion, not that he supported changing it. So, "thats the way it is" when we're dealing with additive all-in bets.