By having that as a parameter rather than a trigger it makes the Zapier service cost $25/month (as opposed to free). I'm sure there are bigger users for whom this might be worth it, but to add 5 or 10 people to my mailing list, for me, it's way too expensive, and I know many of your users are also smaller businesses. Is it possible the Ejunkie dev team might include new mailing list subscribers as a trigger instead of a parameter?
I'm trying to get out of Mailchimp's grip, but it's really hard when so many other products integrate with them for free, but not with smaller companies.