Absolutely, but usually not directly. The loss comes from lost knowledge once everyone moves on to the new thing. How many people know how to tap out Morse code compared to 50 years ago? Who knows the in and outs of steam engine repair? Very few. But these things are lost because they are replaced with something more efficient. I guess my point is the same as kiba, the only way a digital currency could threaten bitcoin is if it was "better." Unfortunately, at this point it seems entirely possible to convince people a replacement is better because it is easier to use or has more corporate backing, even if they threw out some of the IMHO better qualities of bitcoin.