There are good and bad things about both forms of language. The fact that people use more complete sentences in text than they do in speech is probably because they weren't using an analogous form of written communication. I use complete sentences here on FES for the most part but if I'm in an IM window, I don't need to, and the conversation can change so dramatically that in some cases, I would always lag behind if I did. Do people use more complete sentences in a formal debate where you take turns to present your arguments than in casual conversation? I think they do, though I unfortunately can't present any evidence for this. There's also the fact that spoken communication, especially in a face-to-face situation, makes it many times easier to convey emotion, sarcasm and subtle undertones than text does. I'm not going to go as far as Irush and say it's impossible, because I know it isn't, but we have all failed to catch ironic statements in writing where we would have noticed by tone of voice.