Art.250.140{3)allows for a type SE uninsulated grounded conductor to serve as as the egc for ranges and dryers in an existing installation.Why does the code not allow for other wiring types{ie.typeNM}as long as all the other conditions are met?Just wondering.

This question has been asked many times, and when the NEC Panel 5 reviewed the proposals to allow the use as you describe a long time ago, they said "we have got to stop somewhere", they knew there was "no technical reason" though, just that they "did not want to expand on the wiring methods."

Also the "Romex Code Article" says that the EGC is to be used for EGC purposes only.

"Equipment Grounding.
In addition to the insulated conductors, the cable shall be permitted to have an insulated or bare conductor for equipment grounding purposes only."

Thanks Joe, I didn't think that there would be much of an explanation for not allowing it.

My comment is more an effort to ensure I'm understanding this section rather than an espousal of a correct interpretation.

tx: "250.140(3) ....allows SE ...in an existing installation..."

I think the key here is "existing installation"....for years the code has been reducing/cutting back the permissible use of the ground conductor to double as an EGC. In 1999 there were more revisions to this area of the code with the virtual elimination of doing this (ground/EGC)for future installations [250-134, 250-138)...so this is not so much as letting SE 'get away with it', but finally closing the last loop hole of letting any wiring types 'get away with it.'
I'm not old enough to remember, but it is my understanding that 'in the old days' these other wiring types were used to some degree to double up the grounded conductor/EGC; and for other appliances than just those presently listed in 250-140. As time goes on 'accepted wiring methods' change, and some methods just hang in there for no good reason.