Apple's 12.9-inch iPad Pro goes on sale tomorrow, and that means CEO Tim Cook is ready to drum up interest in his company's giant tablet. In a series of interviews with UK publications, Cook has been discussing how a bigger iPad will change the world, but one particular quote really stands out. "I think if you're looking at a PC, why would you buy a PC anymore?" asks Cook, in an interview with The Telegraph. "No really, why would you buy one?"

Cook argues that the iPad Pro "is a replacement for a notebook or a desktop" for lots of people. "They will start using it and conclude they no longer need to use anything else, other than their phones." While it's certainly true that some consumers are replacing PCs with tablets, it's not a trend that has caught on broadly for businesses yet. iPad sales growth has halted, and Tim Cook really wants people to believe in the iPad once again.

There are a number of reasons why iPads aren't selling as well anymore. Old iPads are probably still sufficient for basic tasks and don't need to be replaced, in the same way that PC makers are desperately teaming up together to convince consumers to replace their old laptops. There's also the unavoidable truth that tablets aren't replacing PCs yet. The stats don't lie, and Apple's latest financial results show that Mac sales are up 3 percent and iPad sales are down a staggering 20 percent. Tim Cook can drum up interest in the iPad Pro all day long, but Apple's giant tablet does very little to create a tablet that truly replaces a laptop.

It's easy to see that Apple has learned nothing from Microsoft's Surface work. The original Surface RT shipped with just one angle for its kickstand and it was awkward to use as a laptop replacement on your lap. The Surface Pro is a little better in the lap, but the stylus still doesn't really have a safe home so it constantly falls off. Apple's iPad Pro can only be used at one angle with the keyboard, and there’s no place to store the stylus when you’re not using it.

It also goes far beyond the hardware fundamentals. Apple's iPad Pro ships with a tablet operating system that doesn't have true support for a mouse and keyboard. You won't use a trackpad on the iPad Pro, you'll touch the screen. This means apps are primarily designed for touch. It's Microsoft's problem in reverse: Microsoft lacks the touch apps to make its Surface Pro a perfect combination of laptop and tablet, and Apple lacks the powerful desktop apps to really take advantage of a stylus and keyboard. Both devices are trying to do similar things, but they're flawed right now.

Future versions of both the iPad Pro and Surface Pro will address the obvious usability issues, but Microsoft has already started dropping hints at its own direction. The Surface Book is the biggest indicator yet that a tablet can't replace a laptop just yet. Microsoft's laptop has arrived as Mac sales continue to buck the trend of declining PC shipments. I'm writing this article on a laptop, not an iPad, because it's far more efficient for me right now. Apple's iPad Pro will undoubtedly renew interest in the company's tablet lineup, but it will take a lot more than just words from Tim Cook to convince businesses and entire industries to give up their trusted Macs and PCs.