Well...I had some well-reasoned responses here, but now everything that I post seems to be flagged as spam, presumably because I had the temerity to link to Brad Anderson's blog post about delivering the keynote speeches.
Ooh, that got through.
According to Brad Anderson (who is giving the Keynote) they will "take the wraps off a range of new products and services," at TechEd this year (http://blogs.technet.com/b/in_the_cloud/archive/2013/05/09/teched-2013-big-news-and-a-big-event.aspx ). So it sounds like product announcements, though other MSFT bigwigs are saying that the Windows 8.1 announcements and previews are being saved for Build. I really hope that they blow our socks off. My guess is that they'll unveil the "Blue" updates for for everything but the OSes at TechEd, then unveil the OS updates at Build.