Apple hinted at a possible new feature in iOS 5, automatic app syncing, through a mention in iTunes. The app update page seems to mention such a feature and it enables to Automatic Download in order to get purchased apps and updates directly, without the contribution of iTunes.
There’s no feature like this in iOS 4.3, so MacRumors may be right to suggest that this is a preview of a feature to come in iOS 5. Right now the mention was pulled, so yet another hint to what’s coming on Monday at WWDC 2011. To put it short, if your device has automatic download enabled for applications, the updates will reach your device without the need of syncing.
This doesn’t necessarily mean that you’ll also get firmware updates in the same way, since those are more serious and must be addressed by the user. The only thing that worries me is that such app updates might eat up your data plan without you knowing it, so this kind of sucks.