I lived on Treasure Island during the dot com boom (and bust.) It was an adventure - no comforts of urban living - or even suburban living - but rent was "cheap" and all residents were roughly my age. It was an absolutely amazing time. (These days there are events, flea markets, festivals, wineries, stores...back then, we had...well, we had backyard parties and the 108 Muni. But I digress...)
We had a San Francisco zip code. We had San Francisco Fire and Police. For all intents and purposes, we were a part of San Francisco. But we weren't. We were isolated out there, going to our own parties, riding our own bus, looking out over the bay to the heart of San Francisco.
Digital marketing is a lot of like Treasure Island. For all intents and purposes, it's marketing. But it's not being treated that way, even now. It is isolated within companies (and sometimes even within marketing or communications departments) with its own managers, its own set of rules, its own strategy.
Yes, consumers may have to "take a different bus" to get to your digital marketing platforms - they must get on Facebook, sign up for email, tweet with you. However, regardless of platform, your marketing messages should all be the same. They should sound the same, they should look the same and they should evoke the same responses.
As I've said before, my hope and my expectation is that social/digital marketing will not remain an isolated field. While it takes a different skill set to manage social media, from graphics to copywriting to photography to listening to communicating to empathy, it is still just marketing. it is still one piece of your marketing strategy.