As such, the relationship between the page linked and the page linking is not to be affected by the link. And this is what makes the links not surfacing.
Basically, the current Twitter HTML says: We have no outbound links.
http://support.google.com/webmasters/bin/answer.py?hl=en&...
How does Google handle nofollowed links?
In general, we don't follow them. This means that Google does not transfer PageRank or anchor text across these links. Essentially, using nofollow causes us to drop the target links from our overall graph of the web. However, the target pages may still appear in our index if other sites link to them without using nofollow, or if the URLs are submitted to Google in a Sitemap.
Provided here as information for people who might think you are offering a valid resource:
http://support.google.com/webmasters/bin/answer.py?hl=en&...
[1] http://googleblog.blogspot.com/2007/02/robots-exclusion-prot...
Countless URLs are shared only through tweets, for example URLs that are private URLs to content on services such as TwitPic[1].
1. http://www.dailymail.co.uk/tvshowbiz/article-2084361/AnnaLyn... (NSFW)
This article doesn't say explicitly that it won't follow those links and I would suggest it often will as comments are a rich source of pages to index. The nofollow on a link like this just indicates that the page owner can't vouch for the quality of the linked page (e.g. user submitted link) and therefore doesn't want to pass pagerank to it.
Edit: it's also implied in the parent's link that the META tag only prevents the following of links to pages within your site. This sounds reasonable as who are you to tell Google they can't index a third party domain?
No tweets link to third-party domains, since Twitter wraps all links in their own URL shortener (t.co). Even if you use an independent URL shortener, it will be wrapped by t.co.
(I suppose you could argue that there is no way for Google to determine this algorithmically, since "twitter.com" != "t.co", so it should go ahead with the crawl, but there's the question of how Twitter would respond to that.)
The Google manager blogging about it two years later (five years ago) was probably correct about then-current practice, but I wouldn't count on that as an enduring commitment that Google had never and would never follow such links.