Couldn't it be just perception? I still use an iPhone 3G and I remember I did not want to touch the iPhone 4 when it came out because it was a lot faster than my old 3G and I would realize it even more before playing with a 4. Now I've used a lot a 4S and the 3G is slow as hell, but I would think it is just my perception.
I use an iPad 1 and haven't used any new one for more than 5 minutes and the iPad 1 feels exactly as fast as when I first bought it.
I think the same thing happens in computers. I run a hackintosh machine with an SSD and pretty good hardware and the other day I was putting together an old PC to run MAME (I'm building an arcade cabinet) and god, the thing is slow as hell. I'm sure it was just as slow then I was using it (Pentium D with 3 Gigs of RAM), it just that we are used to be faster now.
EDIT:
Note that new app versions probably ARE slower than older ones in old hardware. If the developer is using the last iPad available to test and neglecting older hardware is what happens. Back when I did native apps we used the best hardware available to develop and low-medium end to test in order to avoid this and optimize our code for speed on not-so-new hardware.
I use an iPad 1 and haven't used any new one for more than 5 minutes and the iPad 1 feels exactly as fast as when I first bought it.
I think the same thing happens in computers. I run a hackintosh machine with an SSD and pretty good hardware and the other day I was putting together an old PC to run MAME (I'm building an arcade cabinet) and god, the thing is slow as hell. I'm sure it was just as slow then I was using it (Pentium D with 3 Gigs of RAM), it just that we are used to be faster now.
EDIT: Note that new app versions probably ARE slower than older ones in old hardware. If the developer is using the last iPad available to test and neglecting older hardware is what happens. Back when I did native apps we used the best hardware available to develop and low-medium end to test in order to avoid this and optimize our code for speed on not-so-new hardware.