One effect of software patents is for people to say "wow that's a great idea! how can we invent around it?" In the prospecting theory, if one guy finds a gold mine, other people try digging around his "claims". But I don't know if that actually happened here.
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.
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.