They poll for updates, one thing you can do is set things like facebook to email you with notifications through an email account that supports push. This way you're notified as soon as it happens.
Yeah I did the Facebook email notifications too since you have more options of what type of notifications to receive and Gmail is push. The Facebook app really needs some catching up to be like the iOS one. I do wish Twidroyd got push notifications or an email option though. I did read on Twitter that the next PingChat will use the push services among other new features.