To extend on your analogy, I'm pretty sure if you started cussing out the bus driver because your mate hadn't paid and got left at the depot, you'd be on the side of the road too.
It all depends on the contract. Presumably, a bus ticket would say something about not endangering or disturbing the other passengers, but if you just, say, tweeted angry messages to the president of Greyhound, it would be a hell of a stretch for them to find grounds to legally void the contract (i.e., kick you off the bus).
0.5% doesn't seem much, but if they succeed in this, many more other patent trolls will come out of the woodwork and all will demand a small percentages. Lots of these quickly add up, with 100 patent trolls parasiting on your App, you lose already half the profit.
