That seems to be the conclusion of an interesting new report from Pew. On political topics, anyway, two distinct groups form on Twitter, and each draws on quite different news sources.
The report discusses other types of grouping depending on the subject matter. I guess social media are a more significant medium [note the proper use of Latin plurals] than I had realized. Nevertheless, I'm not going to start tweeting because I think most ideas worth sharing require at least a paragraph, not just a bumper sticker or similar 140-character expression.