This is sadly true. With just greylisting, spam isn't much of a problem. I get some spam, most of it to an address leaked from the adobe-hack (I don't drop mail to it, I just keep the few spam emails that get through greylisting, for possible future use for training a bayesian spam filter), and some sent to my publicly registered company email (mandated by law in Norway).

It's unfortunately pretty hard to tell the difference between people being slow to reply to mails to gmail addresses, and google flagging your mail as spam for no discernibly good reason.

Anecdotally they don't care about anyone other than gmail users, so there's not much to do about it other than a) give up on the idea that gmail interops with standard email, b) hope that more people move away from gmail, or c) just tell people that you don't care that your email is filtered as spam because they're using an email provider (gmail) that doesn't deal well with email.