Twiiter oEmbeds not displaying Twitter Box

I can’t get tweets to autoembed, am I doing something silly? Others are having the same issue:

http://suzettefranck.me/tweet-test/
http://wpgirlieshow.com/twitter-test/

same thing on a different host.
same thing with or without https
same thing on posts and pages
same thing on different themes
same thing if entered in either Visual or Text tab
same thing if plugins are enabled or not

I’ve run out of things to try, any ideas or experience with this would be much appreciated! 🙂