I still can't view any content without signing in.
This comment thread started with someone explaining why they won't use Twitter, and now you're arguing from the standpoint of someone who essentially doesn't use it anyway.
I can't load tweets on people's profile pages, but navigating to a specific tweet works. That probably kills a lot of indexers.
Probably they just wanted to fix the problem that existing tweets referenced in news articles, etc. were now unavailable, but at the same time keep things locked out to non-account holders generally.