Twitter is not an RSS news replacement; Twitter is an additional socially curated news source.
You can’t rely on your followers to inform you of every nook and cranny in your interests. You still need a personal list of sources.
Sure, blogs and newspapers tweet links but they don’t tweet every link. You’re bound to miss something important if you just use Twitter as your news source.
We need to pull from multiple sources to shape our minds and opinions. The RSS reader is therefore still useful and relevant.