With pinch-to-zoom you have to use 2 fingers, BUT it's faster to switch modes (from panning to zooming) than using swirls.

When you're browsing, generally people have to hold the device with 2 hands anyway, because of the need to type URLs or other text entries... this is even more so with bigger tablet devices where it's not practical to hold with 1 hand.

On the iPad, the pinch-to-zoom actually takes into account of where you're initialing the pinch. Thus you can combine pan/scroll/zoom in one motion.
I think most people will find that most preferable on 7"> slates.