As Seth Weintraub in his article describes - push could be a lot lot more.
App push notification is a (poor) kludge to get around not allowing background apps.
1)
Power usage. Consider the problems even now with push email. Power usage can go way up since you'll need a heartbeat (or a changed-IP client-to-server notification) so that "push" can work.
Each phone will need a second heartbeat for the app notifications. Power usage also goes up because each app has to save its state, die, then get restarted from scratch when a notification comes in.
2)
Potential for mass failures. If you think 3G problems were a mess, consider millions of phones with apps not working right because of Apple's servers being down. And Apple so far doesn't have a great rep (or experience) at keeping everything up 24/7.
3)
Burden on programmers. App push notification requires the poor app programmer to find and maintain their own servers to send notifications to Apple's servers. This major stumbling point seems to get glossed over.
Example of why app notifications can be a dumb solution to the background problem:
Consider writing an app that is supposed to remind someone when and which pill to take. At the right time, it will vibrate and show what the pill looks like. On any other device, this is easy.
On the iPhone, your app must send an alarm request to a server somewhere. The server then must, at the right times, send a notification to Apple's servers, who then push the notification down to the phone, which starts the app so it can alert you.
That's a LOT of pointless work, battery, expense, and potential failure points, for such a simple app. Worse, put your phone into Airplane Mode, and the app doesn't work at all.
Hopefully Apple will come up with a better solution for cases like this. Or perhaps I'm totally off base. Corrections welcome.