> [...] they accidentally infringe on a patent
I hate to break it to you, but chances are that you infringe on hundreds, if not more, patents in the US. Nobody can tell you what or even how many patents you infringe on, though. Nobody has read all the patents and every single one is subject to interpretation. An interpretation, I might add, that has to be validated by a legal system that really doesn't care about correctness, technical validation or even fairness.Patents in the software industry were historically held for defensive purposes. If you get large enough you start building a patent portfolio so other companies can't sue you because you'll sue them back. Everybody infringes on everybody else's absurd patents so suing is a Mutually Assured Destruction scenario (neither party wins and the lawyers take all the money that you could have invested in something worthwhile).
Companies like Lodsys and Intellectual Ventures are different. They only have patents and they have no product. So if they sue you for patent infringement you can't sue back even if you have patents because they don't have a product and by definition can't infringe on your patents (if you have them).
Patent fights between corporations are ugly enough, but are generally on a more-or-less level playing field. They happen in the courts between very well funded armies of lawyers.
Suits between, say, Lodsys (money + patents + lawyers + no product) and independent developers (no money + no patents + no lawyers + product) are so vastly uneven and unfair that most developers will just give up before this ever comes before a court. Even if you want to do it on principle it'll bankrupt your life. Just giving up and finding safer markets with (maybe) lower profit margins seems like the obvious way to go for anybody.