Here's a basic solution to this general problem:<p>To succeed on a patent infringement claim, the plaintiff must prove a causal link between his patent and the defendant's technology. That is, the plaintiff must prove that the defendant either (1) reverse engineered technology covered by the patent or (2) directly relied on the patent itself in creating the infringing technology.<p>In other words, <i>independent invention should be protected</i>. If I get a vague patent that could arguably be construed as covering in-app purchasing, and ten years later you, in no way directly or indirectly relying on my patent, implement an in-app purchasing system, I should not be able to recover any money from you, since I in no way assisted your technology. I just happened to have gotten lucky in that I secured a patent with vague language that could be construed to cover a basic piece of tech that 10 years later became popular.