Look, the real issue is simple: all of these "web startups" are not very innovative. All of them are roughly the same: ever so slightly more novel way to deliver roughly the same set of data to users in exchange for app or token of money. How is that "ground breaking"?
Thing is, when everyone is doing roughly the same thing, which costs perhaps a few engineering months to build, how can startups ever compete with the big guys who are hell bent on ensuring their success? It's like trying to open supermarkets to compete with Walmart, or building gasoline car to compete with Toyota, except it's cheaper for the Big Five to copy than for Toyota, because the media (information) is inherently more traceable.
I remember when Windows 98, XP, Google, Gmail, Prime (and Uber, eBay, and paypal) came out. They blew everyone's mind. They changed how we work and live. What's so hot about SnapChat? I mean, it's probably ever so slightly more entertaining than, says, Hangout or WhatsApp, but it's just minor tricks on top of roughly the same set of features. Of course these competitors will drive it out of the marketplace. It holds no long term competitive advantages.
There are businesses that don't deserve to die. For example, a local store provides not just goods, but a community center and an identity for a small town; it gives more value than mere commerce. The decline of these should alarm us. On the other hand, some businesses do deserve to die. And lack of long term advantage, lack of innovation, lack of additional value sounds exactly "should die".