This is not entirely true. Gmail (and other big email providers) blacklist blocks of IP addresses belonging to hosting providers who are perhaps not as proactive as they should be at detecting and removing spammers. If you unwittingly sign up at one of these providers, it doesn't matter how perfect your mail configuration is: anything you send to a gmail address is gonna go to spam. Gmail of course doesn't publish these lists, so the only way to find out about them is to run into one.
I understand gmail's problem, and I don't have a better solution, but it's not just about insecure mail servers.