As a KitchenAid retailer it is my understanding that the internal components of the 2 mixers are identical (there are some other differences; an "orange power cord", slightly different bowl handle, and I think the included whisk, dough hook and beater are made from stainless steel)
One MAIN difference is (apart for the actual NSF certification and the things I mentioned above); the NON NSF machine is made and warrantied for NON commercial use only.
Meaning (this is my interpretation and therefore JMHO), if you are making cakes from your home you are probably good to purchase the NON NSF 7 quart without worry... If you have a bakery or other commercial settings, you may want to consider the NSF model.
On a side note; in Canada (where we are located) the Commercial/NSF model is not available. However, the commercial (stainless steel) accessories are available for purchase...