I suspect it has to do with the browser and other things.Must be your browser or something. Twitter embeds show up just fine.
Twitter embeds don't work with the browser I'm usually using which is FireFox. It could be FireFox or it could also be an adblock program which blocks unnecessary ads (you can tailor it so ads on a site get through, but not ads on other sites...for example...twitter stuff coming through even if you can see other ads on the site).
I can see ads on the Right Side of my screen on ENworld for example, but I only can see like the top of a twitter post (it's like in normal quotes, but doesn't expand so you can't see the rest of it) in the forums. I suspect it has something to do with FireFox or the browser...as you said.