Of course there's some business rationale. Otherwise nobody would be doing it.
See, I think that very few people actually need instant messaging. Twitter is the perfect blend between blogging and IMing. If you're not on it, try it out!
Several Years ago, JetBlue positioned itself as the "cool" discount airline. While SouthWest and ATA offered cheap fares, JetBlue -- through sleek visual branding -- stood out as a company that's not only cooler than its fellow discounters, but than most mainstream airlines as well.