I agree that tablet sales are surging, but I disagree that it's at the PC's expense.
The problem for the PC is that to a large extent, the market is saturated. Most people who can use a PC, have one. There is still a substantial PC market, but it consists of upgrades to and replacements for existing units, not new sales, and that market will not drive the growth the financial markets look for.
Tablets have different use cases, and are bought in *addition* to PCs. The advantage is that they are smaller, lighter, and portable. They can be conveniently carried around, and do a lot (though not all) of what people use PCs to do.
The primary use case for a tablet is to be a media consumption device, presenting audio, video, pictures, and text. They are essentially "half duplex", where you receive far more than you send, and the UI is optimized for selecting media you want to consume. If you need to *create* any amount of content, a tablet will fall down.
I don't currently have a tablet, but if I acquire one, the first addition will be a Bluetooth keyboard, because on screen virtual keyboards lose for any volume of text entry. Strong preference will be given to a device that can be plugged into a docking station.
We aren't quite there, but the components are becoming small, fast, and cheap enough that I expect to someday be able to buy something about the size of a smartphone which may *be* my primary computing device: I simply plug it into a docking station that connects it to one or more large monitors, a keyboard and mouse, external storage, and my network. Stand alone, it may be my smartphone, or if I want a bigger screen, paired with a tablet when I'm traveling.
(Insofar as possible, critical information would not live on it, but on my network or the cloud, and if it's last or stolen, I simply replace the hardware, plug it into my network via the docking station, and it gets configured automatically to replace the old unit.)
Tablets are good for those with a lot of time on their hands and someone else taking care of the bills - fits the ex - hippy ( & some say dope dealer ) Jobs profile. This would probably cover 80 % of current PC users in the US ( home, school & Starbucks ! ). The rest would have to stay with PCs but would prefer that they become as light and power efficient as Tablets ( i,e. ultrabooks with cheap 200 GB of SSD, detachable keyboards with a second less power hungry processor,...). Intel and MS are you listening ?
My experience is that the non-engineer population and certainly anyone holding a job will replace their device every 2 years or less. People who don't have a car or a house but are making minimum wage will spend 25% of their income on a portable mobile device. Walk into any event that contains people between 20 and 50 and the lions share will be playing on their phone.
The projection is realistic. I want a regular tablet and a smaller travel tablet. ERight now, I have none. Tablets will find their way into a lot of office and industrial applications as a smart platform. A cheap smart product with wireless connectivity can be used all over the place.
In "Who Killed the Electric Car", Ed Begley Jr. makes the comment: "Electric cars are not for everybody. They can only satisfy the driving needs of 90% of Americans."
What's holding back electric cars nowadays is IMO the high cost, which is mostly because of small-scale manufacturing. Electric cars should be cheaper than fossil-fuel cars because they're so much simpler, and they will be when they're made in as large numbers as fossil-fuel cars. JMO/YMMV
Similarly, tablets can satisfy the computing needs of "only" 90% or so of people as well. Most people want a computer for consuming media, searching the Internet, and occasional e-mail. Tablets easily cover this. Chromebooks capture the next level who want a larger screen and a real keyboard. Only 10% or so need a full laptop or desktop, usually only because they need software that isn't available on a tablet or Chromebook.