It's another fiddle to defend inerrancy.
And totally unnecessary. The phrase used both by the KJV and the NIV actually says "winged creatures that walk on all fours". I think it's just a way of distinguishing creatures that go around in a manner a bit like a quadruped from birds which walk upright on two legs (effectively). That's all. It's technically incorrect (and I'm not sure it's incorrect enough to invalidate any vaguely sensible inerrancy doctrine) but it's not really an issue. Essentially I agree with truthlover's point that the Hebrews could not have really been that daft that they couldn't count legs.
Unless, of course, you want to say that the whole thing is dictated by God and totally and literally true in everything it asserts explicitly or implicitly, which of course is the view from which YEC derives.
[This message has been edited by Karl, 05-13-2003]