People just don't write anymore. Word processors made everybody lazy, and email made us careless. But texting? It spawned a generation whose typical communications look more like vanity plates than personal messages. The average text message (which is limited to 160 characters, here's why) is devoid of substance and vowels. W00t. L8r. Ttfn.
It wasn't the medium that took meaning from the messages, it was the context. Continuing in email's carelessness, texting is casual. We've all collectively decided our friends aren't worth writing for. But what if our texts suddenly weren't so private? Then we'd have to make sure that somewhere beneath those 160 characters hid a clean pair of underwear and a decently constructed thought.
Limited down to 140 characters to accommodate usernames, tweets are meant to be noticed, to attract, to communicate something personal albeit trivial. To fit in your thought, a link, an @reply, and a #hashtag, you can't just spit out whatever words come to mind. To tweet, one must edit.
Sure, most people simply use shorthand to squeeze their lengthy missives under the 140-character wire. But others actually start eliminating that, nixing the passive voice, and axing frivolous adjectives and adverbs.
The bottom line: every tweep or twitterer must edit. How they do it and how well they do it are totally up to them. But Twitter is teaching texters the value of every letter and inspiring them to text with meaning and purpose.
Let your 6th grade English teacher know there's still hope for the future.