This transition from solely focusing on SEO to a more holistic marketing tool is not new. They've been moving in this direction for at least the past year. I think this is a good time for them to make the break from being pigeonholed as an SEO company to something bigger, something more inclusive. SEO is no longer a narrow niche type of marketing, at least not to the people who perform SEO daily or on a professional level.
It's a combination of content creation, site optimization, outreach and relationship building, branding and more. Not all these components are always associated with "SEO", which often times has a negative connotation attached to it. Moz is hoping to capture a larger part of the inbound marketing market than SEOmoz ever could.