Larry hit it right on. Tablets and smartphones are not quite the same device as a full fledged PC but they are part of the same market, and for many people, they fill the bill such that they rarely, if ever, use their PC anymore because they do the things they need. I find that some things are a little tougher with the tablet or smartphone, but others are much simpler. There are still things the PC is needed for, but most things can be accomplished with relative ease.
It all depends on what you are trying to measure. Want to prove that things are looking down? Separate them and talk about how they are cannibalizing each other. If you want the chart to look up, add them together and throw in smartphones as well. Suddenly you have a bull market! Seriously, it seems to me that there is overlap between those categories. One way or the other, the number of devices per consumer seems to be going up.
Tablet's and PC market seem to be somewhat mutually exclusive to me. At one point, analysts have said the tablet may hurt PC sales because of the similarity of the products. Now, with the estimated sales to 2015, the figure does indicate these 2 products are mutually exclusive. One may help the other to thrive. Yet, there is no indication the tablet will eat a chunk of PC market. Any comments?