Scenario A: Google back when they initially developed Android ran into a design roadblock. They saw no way to solve the particular problem until one of the developers read a MS patent that solved their issue. MS is therefore paid royalties on their patent.
It's not about finding a solution. It's about taking what somebody has worked on, experimented with, done usability testing, put in a product and convinced the market to use and have a second company come in and say thanks for all the hard work, in a month we'll have a cheaper clone doing the exact same thing.
Scenario B: Google developed Android without ever having heard of any MS patents.
...and not knowing of any product using any of the MS patents, even if they were unaware it was patented and by who. Particularly in the same business, it's rather hard not to know what features the competition is advertising. It's certainly hard to prove you didn't know about them. Submarine patents are a different story, but for example when they made Android they probably couldn't claim ignorance of any features the iPhone had. Even the business requirements and feature requests can be "contaminated" by other products, it's not a feature you'd have added unless someone else had done it first.
Of course sometimes you get unlucky and develop the exact same solution, but that also means you're reinventing the wheel. Do you want a medal? Or you might feel it's obvious and widespread now, but was it that obvious when it was patented? Ten years ago is a long time in the tech industry, things that I go "well, duuuuuuuuh" to today maybe wasn't. If they were, I'd like to go back and redo my investments. I'm sure you all remember the warm reception the iPod get, boy was that right on the money...