Why the Library of Congress cares about archiving our tweets

For those interested, I asked around and it looks like the entire Twitter collection is only going to be 5TB worth.

I hope they do elect to store the actual URLs when URL shorteners are involved. Really, though it would eat a hole in the URL shorteners' business, I really think sites like Twitter should be dynamically 'fixing' those links before inserting them into the database.

I've been curious. Does this include the tweets of "private" accounts?