Some famous law-suits were about patents that are far less trivial than your bridge example.
For example, Pixar holds a patent on Monte Carlo sampling, and has sued or threatened a number of companies that used any sort of randomization in their rendering algorithms. This despite the fact that Monte Carlo methods have been known and used for many decades before Pixar was started. The issue here is not that the concept of Monte Carlo integration is trivial, but instead that Pixar's contribution to it is so tiny compared to the previous state of the art that it should not give them a "right" to own the whole field.
Similarly, some lawsuits were about compression algorithms if I remeber right. Same issue here - it's not that a given compression algorithm is trivial, it is more the fact that it is probably a tiny increment on the top of existing compression techniques, and anybody that also builds on the known ideas should not be threatened by loosely related patents.
Of course, patents are a problem that should be addressed, but I don't think trying to prove that software patents are somehow different than others is the right way.