@aral At least for Twitter, this is not true. Yeah, the page exhorts you to create an account - but it *does* show the post. At least on desktop; maybe it's different on mobile.
@bontchev@aral it doesn't show the comments though, so you can't see the full post if someone divided it into multiple subposts (the 1/3, 2/3, 3/3 thing in replies)