"""The slope of this graph is the whole story. The complicated general purpose computers are at the bottom, and the simpler specialized computers are at the top."""
This is a terrible graph. The Mac has always been a premium niche computer. 28 years ago computing was in its infancy and computers were expensive, unnetworked with limited benefit to the average household.
Compare this the iPad / iPod Touch and iPhone. These are main stream devices that achieved immediate traction. It is unrealistic to compare Mac sales with those of main stream devices.
You then have the desktop market as a whole. If you compare any single company or brand of desktop against iPad sales, desktop sales would look in trouble. However, if you compare desktop sales to tablet sales it is clear that tablets are still only in their infancy.
BUT TABLETS ARE SELLING FASTER THAN DESKTOPS!
I don't know if this true but it doesn't matter and it doesn't say much about the state of desktops. Everyone has a computer, the market is saturated. No one has a tablet. It makes sense that tablet sales would rocket.
Buying tablets also make a lot of sense for people who just consume content. The fact is though that the iPad isn't great for productivity. It is far better for consuming content. This is what most people do.
However if you want to program, edit images, write a novel, maintain spreadsheets, make movies etc a desktop / laptop is what you need.
The PC isn't dead and it isn't dying. It has reached a point where people only buy replacements. Now yes, some people may switch perminantly to a tablet. Thats fine. For the forseeable future though there will be a large market of business and consumers who require more than a tablet can provide.
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The article also touches on how great the new iPad screen is. I don't think its all that. I walked past the demo of 'the new iPad' twice before asking a sales guy to point to which one was 'the new iPad'. Yes, if you put the screen close to your face you see less pixelation on icons. For general web surfing though I saw no perceived difference. Hell, I don't really see any pixelation on my iPad2. Perhaps I am not holding it close enough to my face...