Microsoft, like Apple, implemented a system that tries to maintain a sole connection to a server that handles all the various application requests. The reasons are supposed to be better battery life and improved time to market for developers toiling away at their SDKs, but with Android, who opts to follow a different route and makes developers use their own notification system, but shove their notifications inside their top drawer like notification bar, battery life doesn’t seem to be an issue. In fact, battery life with Android gets better with every new version of the operating system.
Personally, I had to disable both push email and push notifications to get more than 12 hours of battery life out of my iPhone 4, so I don’t buy the improved battery argument. Some platforms are simply better built to cope with multiple concurrent connections.