Yesterday, Twitter and the tech blogs were all of a flutter about a 128GB iPad. The problem, it seems, is that this thing is hugely expensive. That's OK--you're not going to buy one.
Their own way
First thing to consider about the iPad is that iOS is the only mobile operating system that does not provide a way to expand its storage. (Although some devices like the Nexus 7 don't have a slot, the OS provides a way to do it.) That means that if you happen to need a ton of onboard storage, Apple has to solder it onto the logic board when you buy it.
A Surface RT, for example, can come with 64GB of onboard storage, but you can buy a 64GB microSD card for it for some small amount of money. But this is not an option on the iPad. If Apple just allowed you to plug in a microSD card, this whole thing would be a non-issue.
Who's it for?
Typically, enterprises that buy a bunch of iPads as an application platform typically buy the latest version (always the big one, not the Mini), and in virtually every case buy the 32GB version in black. They also typically don't buy a cellular modem option.
Businesses tend to buy 32GB to give them some expansion room. If you're buying a couple of thousand iPads, because the memory is not upgradable and because you want them to last a few years, 32GB gives you a bit of wiggle room. So why the huge leap to 128GB?
It's simple--there are plenty of complex, specialised situations where you don't have very good connectivity and need a large local cache.
Say you're doing workshop-based training in a bank branch. The instructor asks you to watch a video and complete a short exercise. A 32GB iPad is fine for this because you have Wi-Fi connectivity, and a nice, fat pipe out of the cloud. Streaming the video in this arrangement is fine--you don't need much local storage.
But say you're responsible for commanding an operation to put out a fire in a remote chemical plant? You're going to need a ton of documentation to do that job, and maybe have absolutely no connectivity. Even if you do have connectivity, time is of the essence. A colleague who's suffering from chemical burns doesn't need to hear excuses about "2G being slow" whilst the paramedic is trying to download information on how to treat him.
And there are tons more of these examples where you have very specialised problem domains and either problematic connectivity or would rather not use what connectivity you have. For example:
High resolution medical imaging: You might be working in a hospital with amazing connectivity and pulling massive images off of a server is a doddle, or you might be working in one in the middle of a war zone where investing in IT infrastructure is not the primary concern
Electronic flight bags for pilots: A normal paper flight bag (containing the paperwork and charts needed for a safe flight) weighs 40lb (18kg). On every single flight, every day, worldwide--that is a staggering amount of carbon footprint to spend just moving paper about. Lee Armstong, technical director at the software company that makes the popular Plane Finder app reckons they track 35,000 commercial flights each day. Average weight of a European is 156lb (71kg)--so that's about the equivalent of about an additional 9,000 passengers per day, just wasted carting paperwork about
High-end video or music multimedia work: Not my area, but I presume there are cases where you have large chunks of data to slice and dice around locally and you're using a device like an iPad rather than a traditional workstation to do this.
To reiterate, this is always specialised work. Most people don't need this much local storage, especially not when connectivity is getting better, generic cloud storage is getting more mature, and content providers are getting more capable. For example, now if I buy MP3s from Amazon, it goes straight into Cloud Player and I never need a local copy at all. Categorically, though, this type of lightweight domestic use is not what a 128GB iPad is all about.
There is another point to all of this, which is that this is just how the market works. Any number on a spec sheet gets pushed up over time, whether it's the amount of persistent local storage, main memory, screen resolution, whatever. Give it enough time without the appearance of a 128GB iPad and people would have been complaining that Apple didn't have a 128GB iPad.
Although maybe not--it could be that because of the maturity of cloud services and the drive toward "the cloud is your hard disk" both in the PC and post-PC worlds means that local storage becomes less relevant. My Chromebook only has 16GB of local storage, but because of that specific design of that device as being just a cloud terminal, I'm not sure it matters.
So, the 128GB iPad is not for you. Unless you like to buy the top-end model of every gadget on the market, in which case Apple is waiting for your call.