Brent Simmons, the creator of NetNewsWire, lists some reasons why RSS is still so great even today. You should head over there and read all of it, but I especially thought the two items concerning "Twitter as RSS" were great:
There are no user caps. No company can tell your favorite app how many users it can have. (Twitter does this.)
Nobody can tell you how to display an article from an RSS feed. (Twitter does this with tweets.)
