I think that as far as longevity goes, both music and startups can vary in how long they maintain audience interest. For instance, there are still people today

I think that as far as longevity goes, both music and startups can vary in how long they maintain audience interest. For instance, there are still people today who like to listen to classical music, but that audience is still much smaller than the audience who likes the latest pop star. The Beatles have maintained a very loyal audience base, but as far as sales go they too are no longer the most popular. Just like music can slowly lose popularity as new generations become interested in new genres, so web apps lose popularity over time. But I think that decay is greatly accelerated by the fast moving nature of technology. Therefore while 50 years doesn't move the Beatles into obscurity, and a couple hundred years doesn't completely erase interest in classical music, just five or ten years can sweep away a web app and replace it with something new. It might be possible to create a startup which tries to maintain a small, very loyal group of people who love the startup from the start and continue loving it as it is for a long time, but just as in the music industry the best results are achieved by constantly updating the style and techniques to match what people want today.