These bits of data all live outside the 140 character "limit."
Every good idea people come up with for Twitter involves latching a new piece of metadata to a tweet. And in the middle you have a conflicted, slow and arbitrary (and opaque) decision-making process, controlled by one company.
Shouldn't the architecture of tweets be open to any kind of data that anyone thinks of?
If you make a Twitter client please, start pushing your users' updates to a RSS feed on a server outside of twitter.com. It's just a backup. That's the first easy small step down the path of free evolution. Once someone does that, there are more steps.
To get an idea of what's possible, I recommend reading A better design for Twitter retweets. Wouldn't it be great if we didn't have to wait for Twitter Corp to try this out?
http://bit.ly/5Ve3a2