Karplus-Strong is a really interesting example for the effect of software patents. It is a very efficient and powerful algorithm (3 voice polyphony on a Z80), but it has never been used in any successful instrument. IIRC only one commercial synthesizer manufacturer licensed the patent, but only as a defnsive measure without actually using it in a product. Just imagine all the musuc that might have been without this patent.
PS: the patents, from 1986 and 87 would have expired by now - they're linked from the bottom of the wiki entry: http://en.wikipedia.org/wiki/Karplus-Strong_string_synthesis
BTW: I remember physical simulation synthesisers were available roughly 20 years ago (I don't know if they took off or not - one had a saxophone mouthpiece, and it sounded unbelievably realistic). There's usually more than one way to do it.