This is...completely missing the point. It honestly blows my mind how often exemplars of the Dunning-Kruger effect make it to the top on HN. You know that feeling you get as a programmer watching, like, two people code on the same keyboard on CSI or whatever? That's the feeling anyone with expertise in a domain other than programming gets when reading comments on HN regarding said domain.
The most fundamental appeal of the Push is that it is a very nicely-integrated hardware controller, and -- this is the big thing -- has physical knobs, buttons, pads, etc, a massive selling point to loads and loads and loads of musicians.
An iPad by definition lacks the latter, and will never approach the integration of the Push no matter how much work you put into whichever controller app you're using (TouchOSC, etc). And that's even before you consider the fact that the Push also doubles as an audio interface.
Literally no one in the Push's audience is looking to replace/upgrade the Push's hardware. No one cares what CPU it has. I'm honestly surprised that Ableton published the specs, because it just doesn't matter. It's not a "computer" (even though, yes, technically it is indeed a computer). Depending on which model you buy, its raison d'etre is as an accessory to a computer, more specifically a very specific application; or an appliance designed to run one app and one app only. You might as well be saying that you'd rather buy an iPad over a Tesla because the iPad has a better CPU.