I'm fairly certain that 3000 merchants are active merchants, and 0.9% is out of global accounts, including inactive merchants. I could be wrong, however. =)
I have hard time believing that in the past couple months they could have found >3k people out there looking for a subscription billing solution like this. I think there's definitely a market for it (since I'm part of that market), but I don't think you're talking about millions of potential customers. And even if it is larger than I imagine, it takes time to reach them all.