Possibly they don't patent because, one, their Split Pivot suspension, used on the Salsa bikes, is licensed from Dave Weagle so it's not their own original design to patent. It appears that all of Salsa's FS bikes use the same split pivot suspension design. Surly, Heller, and Foundry don't have any FS bikes, Salsa is the only brand of QBP that has FS. Two, you really can't patent frame geometry, at least not that I've seen. Anyone can put together a frame of various dimensions and angles, there is nothing unique about that.
As a Mechanical Engineer myself and some experience with patents within my company, it makes me wonder, how much actual "engineering" they do at QBP compared to other mainstream big brands like Specialized, Trek and Giant.