As others said... no. And yes.
No, it's not by hardcoded interval. No, it's not a fetch with an immediate reply and then a long dead space.
Yes, there is a request every X minutes, X being dynamic, depending on network conditions. In other words, if it takes a ping every 5 minutes to keep the connection alive, and the Exchange Server settings allow going that low, it will do so. Or it could end up as every 30 minutes. Or 45 minutes. Whatever it takes to keep a connection alive.
The phone sends the request to the server with a timeout. Then nothing happens until the server either has a response (email/etc "push" notification) or the timeout is about to expire. (It MUST reply either way, or the phone will think the timeout is too long and lower it.)
The upshot is that the "push" should in theory occur as fast as with the Blackberry.