Amazon's reinvent conference[0] has been going on over the last few days, it's an obvious time/place to announce.

[0] https://reinvent.awsevents.com/

Bezos said recently that he thinks AWS could be Amazon's biggest business. http://techcrunch.com/2013/11/13/jeff-bezos-believes-aws-cou...

From the press conference reported in the link: "Jeff is very excited about the AWS business and he believes - like the rest of the leadership team does – that in the fullness of time- it is very possible that AWS could be the biggest business at Amazon."

Well , the new plethora of updates are centered on AWS since AWS:re-invent is going on at present. Historically, that is when Amazon likes to release new AWS services.