I believe part of the brand loyalty with Apple is that a far higher percentage of people have paid apps on their iPhones than on Android. Once you've paid for a bunch of apps, you are far more likely to want to extend that investment to your next phone.
Sadly I don't have any statistics to back up this belief, but I've spoken to a few friends with iPhones about this in the past.
Again, just my opinion, but if the question had been "Will your next phone also be an iPhone?", I think 67% of iPhone owners would have said yes, whether the iPhone 5 was launched or not. This is why they say "yes" without knowing the spec of the iPhone 5. They don't need to know they spec.