The glass panes used in iOS devices as of late are actually not Corning's Gorilla Glass, though they are based roughly on the same material and so on. There are similarities, but they are most certainly not Gorilla Glass from what I have gathered.
What it all boils down to is impact resistance and durability. Gorilla Glass was better at those things than both the iPhone 4 and iPad from what I have read and seen. Then the iPad 2 came, and the iPad 2 glass, despite being thinner, is actually a lot more durable than the first iPad's, possibly hinting at that it's a better glass technology than Gorilla Glass.
So it really depends on which device you are talking about.