Steve Jobs was quoted as saying 'I think PCs are going to be like trucks. Fewer people will need them.' It seems to be happening. However, in my mind there has been a significant evolution of the tablet landscape in the first 4 years since the iPad's introduction. And I believe this may have a bigger impact than we currently realize on what role tablets and PCs will play for people in the future, and what other PCs or devices we may use.
It might be obvious at this point, but to me it's looking more and more like tablets that you can easily hold in one hand will become the future of tablets, while larger tablets will merge with laptops and also include a detachable or even an attached keyboard. This means tablets of about 8 or 9 inches, but not nearly as wide as the original 9.7 inch iPad. And certainly not larger screen sizes of 12 or 14 inches that are used for laptops with keyboards built-in. Instead, these larger 10 to 14 inch tablets will merge with laptops, while tablets of 8 or 9 inches will really be the largest pure tablet size. Again, phones and pure tablets will be devices you can hold comfortably in one hand. Larger "tablets" or laptops will more likely include a keyboard, unlike the original 9.7" iPad.
If this happens, it could mean that a tablet may not be as good at completely replacing a PC or laptop as some people were hoping. Basically, as smaller tablets become more popular, it becomes more likely that more people may also need a laptop or desktop PC with a keyboard, even if it also includes a touch screen like a tablet. Meaning, the small tablet may not be their only device, and may not have a large enough screen and keyboard to do everything they need their main computer to do.
When the 9.7 inch iPad was created we couldn't have known exactly how it was going to be used. What all could you use it for? What couldn't you use it for? Would it replace a laptop? Would you use a keyboard? How easy would it be to hold in one hand? If tablets are cars, maybe the original 9.7 inch iPad could be the Ford Model T. Not changed significantly for a while but eventually being phased out. Maybe a better comparison would be the large-sized cars of the 60s to 90s that many people drove. Those models of cars are still useful but were eventually replaced for everyone by smaller cars. Maybe this happened when it was realized that if you didn't have a truck or a minivan, that the extra bit of room didn't bring much value over a slightly smaller and cheaper car for what you needed it to do.
There are many reasons why 8 inch tablets that you can hold easier may become the de facto standard and 10 inch tablets will become much less used. The success of 7 inch Android tablets. The ease of use of smaller e-book readers. The introduction of the iPad mini with retina display. The failure of Windows 8 to create the everything laptop and tablet hybrid with one unified operating system. The rumours about the next versions of Windows putting more emphasis on the desktop interface again, presumably for laptops and desktops. The fact that Google has not tried to make Android a desktop OS. The trend for phones with much larger screen sizes so that people might not need a phone and a tablet. Maybe most importantly, having a tablet, phone, or other mobile devices you can easily hold and carry in one hand has turned out to have many advantages over larger tablets like the original iPad with its 10 inch 4:3 screen.
It might not be exactly what Steve Jobs wanted, but sometimes you just can't know how people will use what you create. It often evolves and through trial, error, and use by actual people you mold it into something useful. Turns out, that new mold might be a slightly smaller 8 inch tablet that can fit in your hand, or a larger "tablet" that is more like a laptop computer and has a physical keyboard. And with a keyboard and a larger screen you are blurring the lines between whether it is a car, or is actually a truck that is just easier to use.
So if I'm correct, we've found out by trial and error between Apple, Microsoft, and Google what the best size of a tablet is. You can hold it in your hand easily and type on it with your thumbs. To me, the biggest effect of this is that more people who tried to buy 10 inch iPad tablets or 12 inch Windows 8 tablets as a do it all laptop replacement will start to buy more 8 inch tablets. Many of these people will still need a truck. A laptop or a desktop PC with a screen larger than 8 inches, and a keyboard and stand built-in. It will likely include a touch screen like a tablet and simpler software like a tablet. But with a larger screen and an attached keyboard it might be just as much a laptop as it is a tablet, or just as much a truck as it is a car.