Two fingered scroll becomes necessary when a web page uses a iframe or other element to display scrollable content. With just single finger touch gestures Safari can't* know whether you are trying to scroll the page or the content of the scrollable element.

Hence the rather clumsy two finger scroll.

I'm curious to know how Android's browser handles this case ?

* ok, in some cases Safari probably could work out what you were meaning to scroll, but when you factor in the number of times it would guess wrong the two finger scroll is the less of two evils. In practice I rarely come across cases where I need to use the two finger scroll.