I don't know that there is a difference in the motors between the two saws...I personally doubt it but that's just a guess. I've read that it's a function of the new thinner kerf blades along with a different tooth geometry in the new blades.
I'd not advise removing the riving knife in the older saws, a better solution would be to reduce the thickness of the riving knife to better match the thickness of the newer blade.
Better yet, if that's an important feature to you...just purchase the new saw and put the older one down the road. You will probably be able to recoup 80% of your original purchase price and then no one will be afraid to answer questions. [smile]