This is a bold statement.

First, one can spoof udp packets in the same way as tcp segments. Think syn or ack floods.

Second the Krebs ddos is said to generate over 600 gigs of traffic but it was not necessarily with fully established tcp connections. It's unlikely it was with valid tcp connections.

Let me give you a thought experiment: if you are flooded with 600 gigs of forged tcp packets, how do you know if the source ip's are spoofed or not? How do you know the ip in the src ip field belongs to the one that originated the packet?

Flatly incorrect. The latest and largest attacks are generally UDP reflection attacks, with a smattering of TCP SYN flood & pure L7 attacks thrown in.