Perhaps, then, twitter is not a malady but a symptom. The idea that we can whittle all of our ideas down to 140 characters has been building for decades, as you say, and only now manifests itself explicitly.

I don't think it's too nostalgic to pine for longer, epic exhortation of ideas. People still give memorable speeches (cf. Obama's "More Perfect Union"), and people still memorize the speeches of old. They give context to the soundbites and give depth when we want to go beyond the misquotes. But yes, blaming twitter goes too far, because it certainly has its place, too. It's just another tool of communication that has its benefits and pitfalls.