You're right for the most part, but I hope that will change soon. I've been working on a new spam filter for a while, it's in testing on my mail server for a handful of customers, and quite a bit of stuff from constantcontact, sendgrid, Amazon, and even Gmail are getting caught by it.

The unfortunate thing is that every time there's a new trusted mailing service with a good reputation, spammers flock to it.