At first when I read this suggestion I thought it didn't seem like something to include. This would force every smart phone to support this type of scrolling wouldn't it?
I think there's an issue with many developers just doing too much on mobile web without realizing the limitations of the device they're using.
People today are used to developing on systems where they don't have to think about memory, hard drive space, or performance. But when you get to mobile web you have to think about these things AND more (screen resolutions, landscape vs portrait etc).
The problem with many suggestions for w3c is that they are often tied to what specific companies (ahem Apple) are integrating (or not).
In terms of the Facebook app, I (along with many others) have just been flabbergasted that they've not been able to make their app load fast. Tobie's post gives some great insight, but I don't think it's impossible to create a smooth, well run webview - especially when you have the resources Facebook has.