Is there really a difference?
From my reading, research and use in the field, I would say yes.
Alpaca fleece is as soft as cashmere, warmer than sheep’s wool, hypo-allergenic and almost completely waterproof. This is the tag line I hear most often in the alpaca world. I am going to dissect this phrase comparing the two fibers.
Alpaca fleece is as soft as cashmere: Sometimes. Some alpacas can also feel as cuddly as a Brillo pad. However, many farms promote quality breeding programs with super fine, 16-18 micron fleece, which is extremely soft. Plus, alpaca does not have the scales that wool has, so the strains are smoother. Wool production has made great strides in increasing the softness of the strains of various sheep herds. This is evident in a company call Rambler's Way with great wool products.
Warmer than sheep’s wool: Alpaca is a hollow fiber, where sheep wool has pockets of air. Much like Polar Bear fur, the air pockets allow for heat to be trapped, creating greater thermal capacity. Thus, alpaca does tend to be able to be warmer than wool.
Hypo-allergenic: Alpaca is considered a dry fiber, without lanolin that is found in sheep’s wool. Some clothing lines of wool are now being promoted as “superwashed” for next-to-skin capabilities by removing the wool’s lanolin and barbs. According to Textile Chemicals: Environmental Data and Facts, the superwashed wool is treated with synthetic resins (polyamide / epichlorohydrine or polyurethane), a method that can include such chemicals as chlorine and hypochlorous acid, sulphuric acid, sodium hypochlorite, alkali metal salts of dichloroisocyanuric acid (DCCA) and an acid-stable wetting agent. The chlorination process for wool has lead to enormous environmental problems. Alpaca now offers an eco-friendly alternative to natural fiber active wear.
Almost Completely Waterproof: Yes, if you pour water on alpaca, it will get wet. However, it does offer great wicking abilities. Wool will absorb up to 50% of its body weight in moisture, but after this there is a saturation point and the sweat can sit next to skin, increasing discomfort and likelihood of blisters (socks rubbing against the skin). Because alpaca is hollow, it traps in more heat and mechanically pushes the water away, never having a saturation point on the skin. Essentially, the water evaporates because of the warmth of the alpaca.
So the answer to my initial question, is there really a difference? Definitely.