Why tablets aren't replacing the PC anytime soon

The tablet has had a remarkable run the past few years. But it is important to note that in the majority of use cases Cheap Tablet PC are not replacing PCs but rather are extending the life of PCs.
We know from our data as well as a number of other firms research that over 90% of tablets sold today have been sold to existing PC owners. And in nearly every supporting data point I have, those tablets are being used to accompany the PC not to replace it. (By PC, I generally mean notebooks).
So it begs the question whether the tablet killing the PC is a valid narrative or not. I'd contend that this is not a valid narrative and more importantly it could affect tablet sales to a degree in 2014.
A key point about tablet sales is that the vast majority sold are 8" or smaller. Which means that by sheer majority, the vast number of tablets bought by consumers are not even contenders to replace the PC. In fact, when you look at tablet usage data you notice that they are used heavier during the evening hours while PCs are used heavier during the day time / work hours.
Think of it this way: PC by day tablet by night. Oh sure, lots of people use their tablets during the day for both entertainment and business (e.g. sales people and other road warriors) reasons, but I think this sums up the use case for most tablet owners.
Now, if we acknowledge the point that the vast majority of tablets on the market are used in conjunction with PCs then we acknowledge that the PC is still used and valued by a large number of consumers. If this is true those PCs will still need to replaced. So the question then becomes when will this happen and could it have an effect on the tablet market?
The evidence is clear that 2013 was the lost year for the PC. One of the steepest declines on record as it has been a stable growth market since the early 2000s. We believe that 2014 could mark a turnaround for the PC sector and catch many by surprise.
Part of the logic for this is the number of PCs in the market being used which are 4 years or older. Depending on whose estimates you use, I prefer my own, the number is around 300-350 million. A good percentage of these customers got away not refreshing their PCs due to their Cheap Tablet PC purchases. Those who have not refreshed their PC for school, work, home, etc., simply can't wait much longer. A PC refresh is coming and as I point out, it could impact tablet sales.