No I'm not being sarcastic - I think calling the apps a skin on top of Safari is a bit of an over-simplification. Most features that users notice happen at this skin layer, not the rendering layer. It's peak HN to really be caring about this especially as Apple offers (as far as I know) no performance difference across browsers using Webkit or w/e. You could actually just say that Safari itself is a skin too, just the default one that comes with iOS.

It's similar to complaining about other basic features of iOS IMO (like complaining there's a default settings app or that iOS just works a certain way).