hi westhawk
there are a couple of parts of the equation and the FADEC is part of the theory...notice I didn't say the more advanced 737's as I'm not sure they havent got FADEC.
As to the DC9...the position of the engines and smaller inlets on the P&W JT8D's make it a bit tougher to get geese into the mighty inlet...the inlet on the 737-2 is still open enough under the wing, but the inlet is smaller and the bird might have missed. (compared to airbus).
But I will say this...a very good pal is a well known aviation correspondent/journalist. He got some stuff off the record from the DOT/FAA...and that's just it, off the record.
Who is going to pay for a massive comparison of engine types and aircraft types and their birdiness? Though it might be P&W's advantage...oh well, you know airplanes well enough to get my off the record gist.