Post title pretty much says it all. As usual Gruber has all sorts of good thoughts on the matter, but still isn’t convinced.
If Apple introduced something like this in iOS 6, they could encourage iOS developers to adopt the recommended APIs to be responsive to changes in available vertical screen space. For now, they could pitch this in the context of shrinking screen space in response to on-screen notification banners, but, come October, apps that do the right thing would automatically be responsive to, say, a new device with 176 more pixels.
Recommended reading as well is this post linked from within the article.