It's a massive overgeneralisation, but you could split iPad owners into three groups:
Those who need the newest items and upgrade every year.
Those who like to keep fairly up to date, but don't necessarily buy every year, maybe every other year.
Those who will keep their iPad as long as they can before spending the money on a new one.
I suspect that the second group is quite a significant proportion. I am one myself, as I upgrade my stuff every other year. These people didn't buy an iPad2, but they are buying now.
Those who need the newest items and upgrade every year.
Those who like to keep fairly up to date, but don't necessarily buy every year, maybe every other year.
Those who will keep their iPad as long as they can before spending the money on a new one.
I suspect that the second group is quite a significant proportion. I am one myself, as I upgrade my stuff every other year. These people didn't buy an iPad2, but they are buying now.