I think that underscores that how much fragmentation exists as brands try to cohesively stitch together the various pieces of their digital footprints. Most companies don't have the luxury (for a lot reasons) to neatly embark on a social media strategy that allows them to start a facebook page, create a twitter account, and so on.
One item that also contributes to that percentage is something that Mashable points out. Some brands skipped the Facebook fan page strategy and dove right into Twitter. I think you'll see those numbers rise as Facebook continues its Twitter-like metamorphosis and brings more publishing and status messages to the web.
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