The difference is that starting from scratch takes patience as depending on flours, temps, and spores in the are where you live, cultivating an active, vigorous starter can take up to two weeks. Starting from a live culture, like King Arthur, is quicker but will still take a bit of feeding and time. A while back on the Baking Bread thread, @dietz199 shared this link to a starter process that does not waste as much flour as the more traditional methods. I used this method at the cabin, and it worked very well.
Sorry for the digression. Back to quick breads!