Agreed. I know there are some issues with people who uses Twitter via SMS but I figured by now they would found an intuitive way to ignore URL's in Tweets.
I often recieve tweets via SMS, and then just type the bit.ly link in, because that's easier than opening up the page of whoever tweeted it and clicking the link.
You can go even shorter with help of one of the TLD registrars, e.g. http://dk./ is a working URL -- you may skip that dot in Firefox and use http://dk/ (Opera will assume you're confused and try to use dk.com).
I confess to knowing very little about the limitations of URLs so perhaps this is s dumb question: why not go all the way down to the shortest possible? Can they just use the minimum unique string of characters? For example http://xyz7g. What are the limits?
Note that silly services like ours ( http://tinyarro.ws ) further compress the character length by using unicode after the / so the URLs never grow beyond 3 characters (and can do 2 characters for a very long time).
Last time I checked, even though the web front end counts characters, the Twitter back end counts bytes (as does, I believe, SMS). So unicode doesn't actually save anything (for twitter).
Conveniently, it does save characters on the website at entry time as their site only checks by character count. Also their backend via website doesn't validate by bytes either.
Their API has fluctuated from checking bytes and characters over time-- I think right now it checks bytes. SMS does it by bytes.
Their API has also done both simultaneously at various times, mogrifying tweets as they transition between queues/memcache.
SMS doesn't actually use bytes natively -- it's 160 7-bit characters packed into 140 bytes. As is their way, Twitter fucks this up: they use the 20 spare characters for the "username: " prefix, but limit usernames to 15 characters -- 3 are completely wasted! Why not allow usernames to be 18 characters?
They've historically fucked up plenty of other SMS encoding details like sending & escaped as & and murdering unicode in weird ways -- always truncating the message at an arbitrary tier instead of validating/refusing it up front.
It's technically possible to put a site on a top level domain. Now that ICANN has started allowing the purchase of TLDs we will soon be going to http://google and we'll probably see a URL shortener at http://l
It's sad that this isn't intentionally a satirical statement.