If you're going to talk about financial/economic phenomena please at least conduct a modicum of quantitative research and give us some concrete data to discuss, not just opinions in a void.
"In 2011, Y Combinator’s poster-child alumni were — already — AirBNB, Dropbox, and Stripe. Can you think of any Y Combinator companies from the last five years as well-positioned today as those Big Three were then? Maybe Instacart, if their unit economics work. That’s it."
"A social network for X, like Facebook"
"A social news site for X, like Digg"
"A way to massively improve your e-mail experience, like GMail"
In other words, people always chase the massive startup that got popular about 3 years previously. This article is pretty much on-time if it's holding up AirBNB, DropBox, and Stripe - those are the massive startups that got popular about 3-4 years ago.
But in 2007, these were most decidedly not the hot industries to go into. Hotels were a done deal: Hilton, Marriott, Holiday Inn, and others chains owned it, and who would think a tiny team could take them on? Filesharing was an incredibly crowded market with 20-30 players, and in any case, if it got popular Google was going to crush them with Google Drive. PayPal owned payments; everybody knew it was a regulated industry with strong network effects, so why bother to compete?