Excuse my entirely naive level of questioning, but to someone who's pretty ignorant of the 'enterprise' world, are they essentially an enterprise-level equivalent of a 37signals or similar?

They say they have 15 million subscribed users, while 37signals merely says "millions", so perhaps 37signals is worth $450m+? Or is there something about companies like SuccessFactors (perhaps big contracts, lock in clauses, or higher rates) that could lead to such large valuations?