yes, i've heard at least a variation of that explanation before, and it made sense for the first few iterations of idevices, but not so much anymore. apple devices are among the most powerful personal computers ever available. it really shouldn't be that way at this point.
iOS animations are not pre-rendered, and more and more they are even interruptible, even interactive. For example, if you start swiping the home screen you can catch the swipe at any point.
That is not necessarily evidence that the swiping animation is not pre-rendered. It just means that if it's pre-rendered, it can be slowed down, sped up and reversed based on the user's finger's motion.
I can tell you for certain that the OS swipe animations are not pre-rendered (you can easily tell, sometimes one or both of the views involved are animated for example), and I highly doubt anyone would do that. What would be the purpose? It's much more complex to handle, and there's no benefit.
It's a frustrating design decision to me as well, maybe because I'd much rather prefer a barebones, stripped-down, streamlined experience, but I'm sure it's more psychologically soothing for more people when compared to the laggy experience on some competing devices.