Compared to the dot-com era, companies are raising negligible sums. Maybe you can get $2M for a failure, but you're not seeing pre-traction companies raising $300M. Similarly, every IPO we've seen has been of a company which actually has real value. Facebook is already profitable and Twitter is seeing real revenue.
Even the Snapchats of the world have a lot more going for them than their dot-com cousins: people actually use them.