I've been saying for years that AWS has secret DDOS protection. Never confirmed, but I'm pretty sure the basic level is just them admitting that they've always had that service.
They have decided to "resolve" this problem by using it as an opportunity to further gouge their customers on bandwidth (which is already 12x+ more expensive than market rate for IP transit), instead of absorbing it into their existing cost structure. Which still would have meant their bandwidth was overpriced, and still would be way higher than what you can get pretty much everywhere else.
For a contrast, OVH provides this protection as an included feature in all of their offerings. Before everyone writes it off as junk in comparison to the glorious AWS black box (AWS is amazing at marketing), bear in mind that the OVH scrubber just took a terabit DDoS attack against it and survived: http://www.securityweek.com/hosting-provider-ovh-hit-1-tbps-...
OVH correctly realizes that the only way to solve this problem is to make sure everybody gets access to it. Otherwise you're just encouraging the democratization of censorship for those without the means to protect themselves against it. I hope the "cloud" providers follow their example.
I switched to AWS 1.5 years ago, and all my DDOS issues magically disappeared overnight.
But yeah, it's interesting to learn there's a baseline anti-DDoS thing that's on by default.