Weight, precision (in most cases), quality materials, but not alway durability, marketing. Now, let me give you my philosophy about purchasing almost anything. I like to buy at level 2, or one down from the top. Usually level 2 products have most of the features, quality and engineering of level 1, but not some of the (perhaps needless) bells and whistles for the marginally large jump in price for what is often the prestige associated with "top of the line." Of course there are exceptions to every rule, but throughout my life I've found this to work out for me. No doubt, owning the top of the line can be good for one's psyche, but in terms of the old pocket book, level 2 seems to be the best value most of the time. That's my opinion... OHB