something like 90%+ of Marketo's customers integrate it with Salesforce. Of course Salesforce won't just cut them off if they have a competitor tool, due to anti-trust issues, but it doesn't necessarily bode well for Marketo now that Salesforce owns a competitor. Pardot is a fairly small piece of Exacttarget though so potentially Marketo could still be a target at some point.
Larger scale B2C marketing automation is generally much more complex than b2b. Ecommerce databases are generally less normalized across businesses, aren't hosted by an intermediary like salesforce and contain more data. Cross-channel retailers with physical stores track a ton of transactions and customers. I really don't think that any b2b marketing automation platform will make much headway trying to go b2c. Hubspot has some success only because they focus on local and small businesses.