Google Reader users have one month left to use the service that they've loved for years, and then it will vanish like so many Google products before it. Companies have been rushing to provide adequate replacements, and have them ready in time. Some are already out there, and others are on the way.
There's no reason to pretend that Twitter can serve as a true replacement for Google Reader, in terms of delivering you every article from every blog you wish to follow, but the company has just made a very significant improvement, which makes it a much more valuable news reader tool.
Update to Twitter lists: You can now make up to 1,000 lists (up from 20), and each list can include up to 5,000 accounts (up from 500).
These are huge differences, and make Twitter's already incredibly useful Lists feature much more useful, particularly for the kind of person that relies on a service like Google Reader. It's now easier to organize your Twitter experience.
It's hard to say whether this move was directly related to the demise of Google Reader, but it certainly makes Twitter an even better source for news consumption, and for those willing to let go of RSS, this could be an attractive option as a primary tool.