Push notifications are tied to an app. Whoever makes the app and puts it in the App Store is responsible for providing push notifications.
In this example, say you created MyRSSApp and distributed it on the App Store. As part of the process when the user sets up their feeds, the app would contact your server and tell it all the RSS feeds it was subscribed to. Your server would note those, check the feeds every so often, and then send a push notification to the correct iPhone when a new feed is available.
Push notifications are just tiny amounts of data, just to alert you to the fact there is some kinds of update or information that an app might be interested in, so suggests opening the app to find out.
If you're thinking that because you provide an RSS feed then you have to provide push notifications too, so that people subscribed to your feed can find out about new posts, this is incorrect. The creator of the app is in charge of t's push notifications.
Hope that helps.